A look at the transmission internals

View with top cover removed. Right side is front - the shifter rail protruding forward into the bell housing with the linkage hanging from it operates the starter switch. It is obvious where the ball at the bottom of the shift lever engages and operates the shifter rails. This is an area subject to wear; I think it is more common that it is the ball on the end of the shift lever that wears down. The tapered pins holding the shifter forks are all safety-wired. Very evident are many brass parts and hence the constant warnings not to use GL5 lubricants in the gearbox / hydraulic / differential compartment - GL5 is said to have additives corrosive to brass.

The shifter fork positions the sliding ring (not sure of proper terminology) such  that when in the position shown, the front and rear gear clusters must turn together.

This is how the gears mesh when they are mounted in place within the gearbox.

The reverse gear cluster and its operating fork. Just to its left are the three spring loaded gizmos that hold the shift rails in place when the tractor is in a certain gear. In the top photo you can see the three holes in the centre in which they sit, and in this photo you see the corresponding two notches in the rail - only two, because the shift lever moves this rail into position to operate the starter, which is momentary.

Rear view of reverse cluster. Within the transmission case there is a pin that fits into the notch in the thrust washer to prevent its turning. All the wear on it thus is taken on the side we don't see. There is a piece of flat stock bolted on the rear of the transmission case that sits in the groove of the shaft, so it can't go anyplace.