A completely failed pilot bushing can lock the input shaft to the eccentric shaft. Been there, done that. It will cause problems on EVERY shift though, not just 2-3. I suspect you have the typical rx-7 tranny problem. Consider running Redline MTL or equivelent. These are actually inferior lubricants that help the synchros work better. Monitor the tranny oil and drain bolt magent when you change oil. If you see more than brass powder, start shopping.

One big caution on the pilot bearing--they are VERY, VERY hard to remove. Mazda has a special tool just for this--do NOT try to use a regular pilot bearing puller! (and yes, I learned that one the hard way too...)

Tachi
#29 ITA SFR