[redmt]

I've never had one of those apart but my guess would be that the pins on the shift rails are loose or worn and the shifter lever arm is slipping between the slots on the rails when they don't line up correctly. The fix would be to replace the rail/shifter dogs and the shift lever arm in the tranny. If this is the case, try and put the lever back into the position of the gear it's stuck in and try and "square shift" it . Of course if that's not the problem forget about what I just said.