A couple weeks before I headed out to Mississippi the driver's door lock ceased working. I could not lock or unlock with the key. Fortunately the other locks worked fine.

I just happened to be in town today, close by my favorite slavage yard and decided to stop by and look for a replacement door handle. Found an '86 420SEL that had just been brought in and opted to pop that handle with the intention of swaping tumblers so the keying was correct. Closer inspection of the latch showed the female end in the lock mechanism was made of plastic, so I decided to grab the inner assembly as well, because if I don't that will surely be my problem.

After getting home I pulled my handle from the door, and much to my surprise I found that the 1/8" roll pin that secures the dongle rod (or whatever you want to call it) had backed out. The result was that even though the rod was seated at both ends the tumbler shaft turned freely in the rod cup which produced no turning action of the rod.

After cleaning the assembly and a seating the roll pin everything works fine. Now I have a complete extra door latch assembly - just in case.