Ok it seems to work well again (actually, better than I ever recall it working since I've owned it). Liberal and repeated application of PB Blaster seems to have freed up whatever was sticking.

The hefty spring at the right of first photo of #14 is what brings the latch back to the open position, when pressing the key button.

I tried it several times and it now works reliably.

Turning the key to the right locks the mechanism so pressing the button doesn't release. Turning the key to the left releases the mechanism so pressing the button releases the latch.

I didn't bother trying to connect up the vacuum to the linkage on the mechanism (too fiddly in there with the tight clearance, and it looked like an exercice in frustration). Quite content to use the key, now that it seems to work as it should and consistently.

Time to put everything back together. Took the advantage of access to spray some anti-rust oil into the bottom edges at the bottom of the inside of the door. Had already drilled some 1/8" holes a few places at the bottom, to allow any water that gets in there to drain out rather than pool and cause rust. My rear hatch is not in great condition (some dents, missing wiper assembly), but it's reasonably solid (as is the rest of the car, which hasn't seen many winters here in the N-E, so is a survivor) and I want to keep it that way.

Thanks for the help and encouragement, and I'm very glad I didn't have to take the sucker out of the door.

Hope this thread and photos will help others with similar issues in the future.

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1983 300TD 240K - 1982 240D 215K - 1996 Dodge Cummins 70K