I had to replace the ignition lock tumbler on 300D last Summer, and so I've been using two different keys for the car, one for the ignition and one for the doors. It hasn't been a problem until this weekend when I stuck the ignition key into the door lock and tried to open it. It took me a few seconds to realize what I had done, and when I switched keys I could no longer work the lock with the correct key. I can lock & unlock the door from the inside using the plunger/knob. But the door tumbler is not turning I have thought about trying to work some graphite into it or even the sander trick for ignition locks. But I was hoping some one might have so insight or experience with such a situation. I really don't like leaving the car unlocked when I'm at work.
Thanks Guys.

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'83 300D (220000 miles and counting)

You've might have jammed up one of the brass pieces inside the lock. I'd pull the lock out and take it apart and make sure each piece it seated properly. Some graphite might do the trick too. Spray some in and push the key in and out several times to see if that will reposition everything properly.

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