This is for the latest version of Morroblivion (v 039). Wrye bash pops up an eror everytime it does anything (build bashed patch, update NPC levels etc.) with Morrowind_ob.esm. The fix is simple. Here is the offending part, per TES4Edit:
[00:00] Checking for Errors in [01] Morrowind_ob.esm
[00:00] DATA - IDLE animation -> [00F8B7DF] <Error: Could not be resolved>
[00:00] Above errors were found in :IdleObjectsIdledrum [ANIO:01F8B823]
[00:00] Above errors were found in :GRUP Top "ANIO"
[04:29] Above errors were found in :[01] Morrowind_ob.esm
The fix is simple, just open 01F8B823 in TES4Edit's search box, and change idle animation "00F8B7DF" to "01F8B7DF". It is the animation for "PlayDrum".
Also, TEs4Edit gives the following while cleaning for UDRs and ITMs:
[Removing "Identical to Master" records done] Processed Records: 429221 Removed Records: 380 Elapsed Time: 00:00
[Undeleting and Disabling References done] Processed Records: 428841 Undeleted Records: 0 Elapsed Time: 00:13
I am using TES4Edit v 3.0.3, which could be different than what you are using David. The previous versions do not give the same results while cleaning.

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