'dieselgiant' has a good write up on subject. Search in the forum for it. There is also a thread that describes the use of a palm sander as a vibrator on the key to loosen it up.

Most people seem to be able to free the key--long enough to get that tumbler out for replacement.

Good luck,

John Bonds '82 240D 4sp, 202k, daily driver (and recent installation of new ignition lock housing).