Slowly rebuilding M41 D type tranny, discovered problem with the extension piece which connects the OD unit to the rest of the tranny. Seems like somebody patched up small areas of inside surface (at OD end) with unknown substance (now cracking and flaking off). They then painted entire inner surface red to match outside. Not sure yet why they attempted this "repair", don't see any cracks forming in metal, or any other defects underneath the unknown patching compound which I've removed.

Question, are the D and J type extension pieces interchangeable? I don't know if
I should use the extension piece I have, especially if somebody tried a mystery repair job, that is now failing. If I end up using my current extension piece, should I remove the red paint on inside surface?