New input shaft bearing every time.

New mainshaft locknut installed with loctite as well as piened.

New main shaft retainer plate / thrust plate. The original was superceded and there is a new PN. The original pounds out allowing the main shaft, as well as the counter shaft to move.

If your thrust plate is really bad, the mainshaft moves far enough to cause the shifter forks to rub. That puts a lot of metal in the bearings and you get very sloppy shifting and or popping out of gear.

The best input bearing is double shielded to keep the metal out.

Shim the counter shaft to the minimum end play but don't preload it.

Take a good look at the OD gears, they have been known to fail. That is the one part that should be checked for cracks. I dont know if where the cracks start can be seen if it's magnafluxed but it might be worth trying.

I would take the OD gear that rides on the main shaft to a shop and get the roots of the teeth shot-piened.

Kevin