Is it a Vacuum leak in my 81 300D?

Since March of this year, my 1981 300D has had difficulty going into reverse. Upon shifting into reverse, the car delays for as many as 30 seconds (sometimes more) unless I rev the engine, and even then the
transmission doesn't grab until 2800 rpm or so. The upside is-once the transmission grabs, it holds the reverse gear. This is a very annoying development. I have tried taking the transmission apart (it appears to be in good shape), I have changed the fluid, and I have used a transmission additive. I am still getting the delayed response. In recent weeks I have also noticed that my car is dieseling a lot more frequently-sometimes for as long as 10-15 seconds after taking the key out of the ignition. Since the pneumatic door locks are also temperamental, I'm wondering if I have some sort of vacuum leak-a breach in the line, or is the canister failing? Can anyone offer me some tips on troubleshooting-or better yet, resolving the issue?
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A failing vacuum pump (on the engine) or a leak will account for the symptoms you describe. The transmission is not in that group. The transmission's vacuum modulator provides the softest shifts with the most vacuum applied and the hardest shifts with no vacuum applied to it.
Given the vacuum leaks the forward shifts will be getting harder.
The transmission's reverse gear has a problem that's independent from the car's vacuum leaks or pump. A reputable transmission shop is the place to fix it; or a rebuilt box from someone like http://www.peterschmid.com/ will fix it.
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