722.315 transmission question

[Graham]

I have this transmission in 85 W123 300D. It makes a loud clunk in drivetrain when shifted into reverse. Otherwise shifts fine.

I am currently replacing 2 yr old axles because they have wear and do clunk. Diff has wear after 460k km, but otherwise seems OK. Rpms normal. Engine/tranny mounts new.

I feel I may be treating a symptom, rather than cause

Given that shifts are otherwise smooth, does anyone here know if there could be a possible transmission issue that would cause just Reverse to have hard shift and cause rear end clunk and lift?