I think a few of us went thru this. Lots of good pix etc.

Bent, loose, broken threaded pin, one of 2 in the shift linkage area.
One in the end of the shift drum stopper?
one that straddles the spring by the shift shaft that runs from one side of the engine case to the other?

Maybe run it in a drill real slow to see the wobble as there is no other real way to check them.

Not a bad fix, just tedious and parts ARE avail