Check the shifter linkage, transmission mounts and bleed the clutch system first, just to be sure. This would be a great time for replacing the tranny mounts too, that's a pretty simple & rewarding job. If the mounts are worn/cracked/gone away, the transmission can wiggle around & bind the shifter linkage too. That'd cause symptoms like you're experiencing.
Start with the simple things first...
The clutch is a pretty simple nuts & bolts job but it's a royal pain in the ass. I'd consider having a shop do it unless I was going to replace everything...output seals, mounts, guibo, shifter cups, Z3 SSK, CSB, etc. The bell housing bolts are way too close to the firewall to make it easy, and the exhaust system is really in the way. Add in thirty years of rust & oil leaks and you have at least a weekend project there.