Ah, my 240d... seems to have every manual transmisson-related problem possible .

So it started with me only having 2nd & 4th. 4th would grind until I 'matched' rpm. 1st and 3rd would pop out of gear when the clutch was let out, reverse would grind while the engine was running.

At some point, a lightbulb went off in my head. If I could shift into reverse with the engine off, then this was apparently a classic clutch-not-disengaging problem. Sure enough, a closer look revealed that the slave cylinder was leaking. Just took care of that, and now I have reverse all the time. Unfortunately, 4th still grinds (though not as bad), so apparently that synchro is toast.

Now on to 1st and 3rd. After much searching on the forum, I found a post by M.B.DOC mentioning that the shift levers were fastened to the transmission with 6mm allens, and if they came loose then the shifting can get pretty sloppy. Sure enough, the 1-2 and 3-4 levers were pretty loose. Tightened those up, and the shifter became crisp and tight. However, 1st and 3rd still pop out of gear, though I can manage to hold 3rd in now.

So maybe loosening and retightening those allens to 'adjust' might help? Kinda at a loss here.