Before you commit to full disassembly, try penetrating lubricants. On my 1994 e320 wagon the driver's door would not give up the key, and passenger door also became sticky and inoperable for locking. I did not see #18 about the miracle MB lock lubricant, but found another one on aftermarket that worked. It's call PB Blaster online or at auto parts stores, been around since 1957, and may need overnight to fully penetrate. We sprayed over and around the stuck key, waited overnight and voila! all keys became tractable in that door again. After applying to passenger lock we're waiting to determine full operability but keys are not grabbed (and that lock is a slave in the system anyway). Good luck!