diff --git a/build-tools/enumification-helpers/methodmap.ext.csv b/build-tools/enumification-helpers/methodmap.ext.csv
index e2dcec1fdc9..2488e8ee818 100644
--- a/build-tools/enumification-helpers/methodmap.ext.csv
+++ b/build-tools/enumification-helpers/methodmap.ext.csv
@@ -1675,7 +1675,8 @@
 26, android.telecom, Call.Callback, onRttInitiationFailure, reason, Android.Telecom.RttSessionModifyResult
 26, android.telephony, TelephonyManager.UssdResponseCallback, onReceiveUssdResponseFailed, failureCode, Android.Telephony.UssdResultCode
 
-26, android.icu.util, TimeZone, getTimeZone, type, Android.Icu.Util.TimeZoneType
+// cannot change this at this state.
+// 24, android.icu.util, TimeZone, getTimeZone, type, Android.Icu.Util.TimeZoneType
 26, android.icu.util, UniversalTimeScale, bigDecimalFrom, timeScale, Android.Icu.Util.UniversalTimeScaleType
 26, android.icu.util, UniversalTimeScale, from, timeScale, Android.Icu.Util.UniversalTimeScaleType
 26, android.icu.util, UniversalTimeScale, getTimeScaleValue, scale, Android.Icu.Util.UniversalTimeScaleType
@@ -1720,7 +1721,6 @@
 26, android.content, Intent, removeFlags, flags, Android.Content.ActivityFlags
 26, android.content.pm, ApplicationInfo, getCategoryTitle, category, Android.Content.PM.ApplicationCategories
 26, android.content.pm, LauncherApps, getApplicationInfo, flags, Android.Content.PM.PackageInfoFlags
-26, android.icu.util, TimeZone, getTimeZone, type, Android.Icu.Util.TimeZoneType
 
 26, android.media, AudioAttributes, getVolumeControlStream, return, Android.Media.Stream
 26, android.media, AudioAttributes, getVolumeControlStream, return, Android.Media.Stream
diff --git a/build-tools/scripts/BuildEverything.mk b/build-tools/scripts/BuildEverything.mk
index d3933ea1cee..65a6fb3c20d 100644
--- a/build-tools/scripts/BuildEverything.mk
+++ b/build-tools/scripts/BuildEverything.mk
@@ -23,7 +23,7 @@ ALL_PLATFORM_IDS  = 1 2 3 4 5 6 7 8 9 10    11  12  13  14  15      16    17
 # supported api levels
 ALL_FRAMEWORKS    = _ _ _ _ _ _ _ _ _ v2.3  _   _   _   _   v4.0.3  v4.1  v4.2  v4.3  v4.4  v4.4.87   v5.0  v5.1  v6.0  v7.0  v7.1  v8.0
 API_LEVELS        =                   10                    15      16    17    18    19    20        21    22    23    24    25    26
-STABLE_API_LEVELS =                   10                    15      16    17    18    19    20        21    22    23    24    25
+STABLE_API_LEVELS =                   10                    15      16    17    18    19    20        21    22    23    24    25    26
 
 ## The preceding values *must* use SPACE, **not** TAB, to separate values.
 
diff --git a/src/Mono.Android/Java.Lang/StringBuffer.cs b/src/Mono.Android/Java.Lang/StringBuffer.cs
new file mode 100644
index 00000000000..777a7a38381
--- /dev/null
+++ b/src/Mono.Android/Java.Lang/StringBuffer.cs
@@ -0,0 +1,19 @@
+#if ANDROID_26
+
+// It is introduced since API 26 not because of new member in StringBuffer
+// but in AbstractStringBuilder which is nonpublic and affects the generated API.
+
+using System;
+
+namespace Java.Lang
+{
+	public partial class StringBuffer
+	{
+		public IAppendable Append (string s, int start, int end)
+		{
+			return Append (new Java.Lang.String (s), start, end);
+		}
+	}
+}
+
+#endif
diff --git a/src/Mono.Android/Java.Lang/StringBuilder.cs b/src/Mono.Android/Java.Lang/StringBuilder.cs
new file mode 100644
index 00000000000..dbc3af843b9
--- /dev/null
+++ b/src/Mono.Android/Java.Lang/StringBuilder.cs
@@ -0,0 +1,19 @@
+#if ANDROID_26
+
+// It is introduced since API 26 not because of new member in StringBuffer
+// but in AbstractStringBuilder which is nonpublic and affects the generated API.
+
+using System;
+
+namespace Java.Lang
+{
+	public partial class StringBuilder
+	{
+		public IAppendable Append (string s, int start, int end)
+		{
+			return Append (new Java.Lang.String (s), start, end);
+		}
+	}
+}
+
+#endif
diff --git a/src/Mono.Android/Java.Nio/FileChannel.cs b/src/Mono.Android/Java.Nio/FileChannel.cs
new file mode 100644
index 00000000000..224ad9d151d
--- /dev/null
+++ b/src/Mono.Android/Java.Nio/FileChannel.cs
@@ -0,0 +1,34 @@
+#if ANDROID_25
+
+using System;
+
+namespace Java.Nio.Channels
+{
+	public partial class FileChannel
+	{
+/*
+This had to be added for API compatibility with earlier API Levels.
+
+It is a newly introduced breakage for OpenJDK migration.
+FileChannel now implements SeekableByteChannel, which never existed, and
+they require those methods to return ISeekableByteChannel in C#, not
+FileChannel whereas FileChannel is ISeekableByteChannel.
+
+So they were first changed in the metadata fixup first, but then it resulted
+in the API breakage. Therefore, I'm reverting the changes in metadata
+and adding explicit interface methods here instead.
+*/
+		ISeekableByteChannel ISeekableByteChannel.Position (long newPosition)
+		{
+			return Position (newPosition);
+		}
+
+		ISeekableByteChannel ISeekableByteChannel.Truncate (long size)
+		{
+			return Truncate (size);
+		}
+	}
+}
+
+#endif
+
diff --git a/src/Mono.Android/Mono.Android.csproj b/src/Mono.Android/Mono.Android.csproj
index 7041a08c91a..63dfa4150f7 100644
--- a/src/Mono.Android/Mono.Android.csproj
+++ b/src/Mono.Android/Mono.Android.csproj
@@ -267,11 +267,14 @@
     <Compile Include="Java.Lang\RuntimeException.cs" />
     <Compile Include="Java.Lang\Short.cs" />
     <Compile Include="Java.Lang\String.cs" />
+    <Compile Include="Java.Lang\StringBuffer.cs" />
+    <Compile Include="Java.Lang\StringBuilder.cs" />
     <Compile Include="Java.Lang\Thread.cs" />
     <Compile Include="Java.Lang\Throwable.cs" />
     <Compile Include="Java.Lang.Reflect\InvocationTargetException.cs" />
     <Compile Include="Java.Nio\Buffer.cs" />
     <Compile Include="Java.Nio\CharBuffer.cs" />
+    <Compile Include="Java.Nio\FileChannel.cs" />
     <Compile Include="Java.Security\IdentityScope.cs" />
     <Compile Include="Java.Util\Spliterators.cs" />
     <Compile Include="Java.Util.Concurrent.Atomic\AtomicInteger.cs" />
diff --git a/src/Mono.Android/metadata b/src/Mono.Android/metadata
index 404d67e2865..1bab91e0d68 100644
--- a/src/Mono.Android/metadata
+++ b/src/Mono.Android/metadata
@@ -77,10 +77,6 @@
   Please use SetSystemScope() instead. This setter is not really public in Android API and will vanish in the future versions.
   </attr>
 
-  <!-- return type in a method in a class cannot be more specific in C# -->
-  <attr path="/api/package[@name='java.nio.channels']/class[@name='FileChannel']/method[@name='position' and parameter[1]/@type='long']" name="managedReturn" api-since="24">Java.Nio.Channels.ISeekableByteChannel</attr>
-  <attr path="/api/package[@name='java.nio.channels']/class[@name='FileChannel']/method[@name='truncate']" name="managedReturn" api-since="24">Java.Nio.Channels.ISeekableByteChannel</attr>
-
   <!-- Also, it seems to lack some non-public types even in android.jar but the derived types still reference...!
     - java.lang.ClassNotFoundException is marked as derived from java.lang.ReflectiveOperationException which does not exist.
     Also, this class has disappeared at some stage. -->
@@ -1362,8 +1358,9 @@
   former non-generic version. So they should be regarded as identical.
   Also, for this method we have *manually* bound generic method.
   
-  We could make fixes in api-merge, but manual fix is 100x simpler. -->
-  <remove-node path="/api/package[@name='android.view']/class/method[@name='findViewById']/typeParameters" api-since="26" />
-  <attr path="/api/package[@name='android.view']/class/method[@name='findViewById']" name="return" api-since="26">android.view.View</attr>
+  We could make fixes in api-merge, but manual fix is 100x simpler.
+  Sadly api-merge is processed before metadata fixup, so it cannot be simple overload removal. -->
+  <remove-node path="/api/package/class/method[@name='findViewById' or @name='onFindViewById' or @name='findViewWithTag']/typeParameters" api-since="26" />
+  <attr path="/api/package/class/method[@name='findViewById' or @name='onFindViewById' or @name='findViewWithTag']" name="return" api-since="26">android.view.View</attr>
 
 </metadata>
diff --git a/src/Mono.Android/methodmap.csv b/src/Mono.Android/methodmap.csv
index c594241a704..2ae5043c479 100644
--- a/src/Mono.Android/methodmap.csv
+++ b/src/Mono.Android/methodmap.csv
@@ -2271,7 +2271,8 @@
 26, android.telecom, Call.Callback, onRttInitiationFailure, reason, Android.Telecom.RttSessionModifyResult
 26, android.telephony, TelephonyManager.UssdResponseCallback, onReceiveUssdResponseFailed, failureCode, Android.Telephony.UssdResultCode
 
-26, android.icu.util, TimeZone, getTimeZone, type, Android.Icu.Util.TimeZoneType
+// cannot change this at this state.
+// 24, android.icu.util, TimeZone, getTimeZone, type, Android.Icu.Util.TimeZoneType
 26, android.icu.util, UniversalTimeScale, bigDecimalFrom, timeScale, Android.Icu.Util.UniversalTimeScaleType
 26, android.icu.util, UniversalTimeScale, from, timeScale, Android.Icu.Util.UniversalTimeScaleType
 26, android.icu.util, UniversalTimeScale, getTimeScaleValue, scale, Android.Icu.Util.UniversalTimeScaleType
@@ -2316,7 +2317,6 @@
 26, android.content, Intent, removeFlags, flags, Android.Content.ActivityFlags
 26, android.content.pm, ApplicationInfo, getCategoryTitle, category, Android.Content.PM.ApplicationCategories
 26, android.content.pm, LauncherApps, getApplicationInfo, flags, Android.Content.PM.PackageInfoFlags
-26, android.icu.util, TimeZone, getTimeZone, type, Android.Icu.Util.TimeZoneType
 
 26, android.media, AudioAttributes, getVolumeControlStream, return, Android.Media.Stream
 26, android.media, AudioAttributes, getVolumeControlStream, return, Android.Media.Stream