The loose allens on my 4-speed's shift levers have taken 1st and 3rd hostage
 

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

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.

Sounds like you may have an internal problem somewhere. Do you know if the gearbox was ever rebuilt? I read that if you don't set the thrust spacers correctly, it can pop out of gear. If the box was ever rebuilt, then that'd explain a worn 4th synchro, cause sometimes only 1-3 are replaced because they see the most use. Do you have the steel or aluminum case?

BTW, I think I've had the worst luck with the manual transmission.