Hello, yesterday I have removed and disassembled the transmission. Diagnosis was 100% correct. Forward clutch was completelly burned. All of the material was gone. Friction discs have welded toghether causing transmission to lock up in reverse an drive forward in neutral. None of other friction discs are burned and are worn by 0.05mm or less.

Now I am wondering what could have caused forward clutch to burn up and friction weld itself. I really dont want just to replace forward clutch discs and have this happen again.

Any ideas on what should I verify before assembling the transmission regarding forward clutch?

Only other thing that I found wrong with the transmission were broken accumulator springs.
Thank you guys very much.