Yeah, I know, "hunt it down yourself". So I'm getting old and lazy. I replaced the doorlock master switch ( the white one ) and all the parts
in the dieselgiant masterkit. I still have a leak.
Scenario 1: Drive.Turn off car. Lock doors. 2 days go by doors unlock fine. Won't re-lock.
Scenario 2: Drive. Turn off car. Run into house to deposit groceries on the kitchen floor. Try to lock car. Won't lock.

Question: Is that eggcrate thing under the cargo area the vac res?

Given the evidence is there an obvious part I should replace or is it one at a time with the MV?

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85 300TD FED-Daily
84 300SD-Wife's
86 XJS-Sunday
66 GMC-Work- Given to my stepson
83 BMW Airhead- Given to my stepson

It sounds like one of your accuator diaphrams is leaking - doors, trunk, or gas filler door. You can trace it down or simply replace all of them. A few years ago, I replaced all of them on my '77 as they were the originals and the rubber is a bit thin to begin with. The diaphrams are not that expensive, so you might want to do the same.

Yes, the eggcrate thing under the cargo area a vac res. There is also another one inside the left fender aft of the wheel well.

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Don't Chrome them; polish them

If one of my acctuators are bad how does it hold vacuum for days AFTER
the locks are set? I can't figure out how a diaphram can pull down and hold but cannot pull down if you DON'T lock the doors quickly. Does vacuum pull them locked, AND unlocked? No pulling against springs?
How can they lock, then 2 days later unlock fine, as long as you do it
in the first minute the engine shuts off?

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85 300TD FED-Daily
84 300SD-Wife's
86 XJS-Sunday
66 GMC-Work- Given to my stepson
83 BMW Airhead- Given to my stepson

Yes the vacuum both locks and unlocks the doors, and it sounds like you have a leak in the unlock circuit. That means the doors will lock fine and hold vacuum, but when you unlock, you lose all the vacuum...can you shut off the engine with the doors unlocked? I couldn't.

The unlock side of the actuators are more prone to leaks (at least on my car) because they have a boot around the shaft that crumbles to bits. If you take the panel off of one of the other doors, you'll see what boot I mean.

Its pretty easy to find which one is leaking, you need a mityvac, and you will be able to pinpoint which door it is by pulling up the carpet on the front driver and passenger floors. Then you only have to take apart the door that is faulty. Here's is a pretty good guide:
http://www.schumanautomotive.com/forums/showthread.php?t=2755

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1985 300TD-euro 352,000 mi
1974 240D (1?)52,000 mi - has a new home now