Hmmm.. Tried the palm-sander-on-the-key trick, which worked for me last year but not last night... Maybe I'll go under the dash or behind the gage cluster and see if I can put a large screwdriver on the tumber/lock mechanism from behind... and vibrate that with the sander. Anybody ever tried something like that?

New cylinder and key set! Genuine MB part! Can it really be no good already? That's why I am thinking it must be something in the lock assembly that is not letting the cylinder turn.

No way will the lock and cylinder assembly come out (cleanly) unless I get that hardened bezel off the cylinder, right? And that won't happen unless I can get it to turn...