if you do you hear any whirring-type noises; or "grating" when the car is in neutral, and the motor is running, it's possibe that your throwout bearing is shot. it's also possible that you have excessive wear in your synchro rings. another indicator of worn synchro's or a bad throwout bearing is poor shift quality. (although, this could be improper linkage adjustment; and that's more easily remedied).
hope this helps. keep me apprised, as i to have a 5spd tranny in my 1986 300E.
[This message has been edited by joebeetle (edited 09-14-1999).]