Stap 13 vertalen
The output 4th gear ("sleeve gear") can suffer from wear. Check the exposed bearing track carefully and the inner bushes. If the inner bushes are worn, they can be replaced, but if the bearing track is worn or pitted, then the gear is scrap.
The other gears should be in usable condition (unless the gearbox has been run with wet oil). Check the case hardening for pitting and the bushes for wear.