I had a leaky vacuum actuator in the coupe's passenger door. The car started not shutting down when the vacuum leak got bad enough.

And yes, vacuum leaks could affect shifting if bad enough.

One thing I noticed was that the system would build vacuum and behave normally when the doors were locked. But in the un-locked position it would not hold vacuum.

So, Out with the Mighty-Vac, which I used to test vacuum circuits from under the hood. Found the reservoir to be good. Confirmed the leak when the doors were un-locked.

I then removed the driver's door panel so I could access the lock and un-lock circuits at the switch in the door. This may have been un-necessary, but it did allow me to verify that the switch itself was not leaking.

I by-passed all the trunk actuators and still had the leak, which localized it to the door. Opened the door and found the rubber boot on the actuator's rod to be cracked.

I scored another actuator from a '84 sedan in the scrap yard, installed, and all is well again. I noticed that MB changed the design of that boot, and also upgraded to a silicone-based material that won't crack as easily.

The idea is to find which system leaks, and then remove devices from the system to localize the leaky item.

Hope this helps!