[Anthony]

After thinking about it some more, I'm not so sure about case expanding as the main problem, although I think it's possible. As I said before, if there is gear misalignment, I would bet that it happens when a load is placed on the tranny, and the input shaft-main shaft junction flexes ever so slightly sideways to cause misalignment between 3rd gear and corresponding counter 3rd gear, before the main case begins to widen.

Don't forget, the main shaft inserts freely into the back of the input shaft, riding on roller bearings, right in front of 3rd gear, so there is always some play, allowing the main shaft and input shaft to flex sideways. My guess, the mainshaft/input shafts flex towards the passenger's side to some degree when a load is placed on the tranny. The counter gear is spinning in a counterclockwise direction viewed from the front, trying to turn the mainshaft 3rd gear in a clockwise direction from the bottom, pushing 3rd gear, and the mainshaft/input shaft towards the passengers side.