I toiled a long time to find the source of my vacuum system collapse. I almost took the plunge and bought the vauum pump rebuild kit... since I couldn't find the source of the problem. However, one spot I overlooked was the through firewall area below the master cylinder/brake booster. I gave a gentle tug on the two vacuum lines that go through there and sure enough, one of them had more free movement than should have been natural. It was the green with yellow strip one that appears to go to the a/c temperature control area. I felt around, found the rubber tubing it goes to and plugged it in. Voila! Problem solved. I had started to go through the diagnostics that were in a previous post but the door looks just felt too tight when I went to unlock and then relock... don't know if that would have necessarily been the case if they were defective or not, but that led me to believe that the problem was still under the hood or the dash. It was, and I'm relieved!! Back to driving the MB!!

Glad to hear that! way to go.