Hey guys, I seem to be having the same problem -- I feel that my brake booster is the source of a vacuum leak. I have narrowed it down by removing the main vacuum line from the booster and plugging it -- then I get up to 20 on the mity vac, and all works great. When I replace the main line onto the booster, the vacuum reading on any of the fittings leading off the main vacuum line drops to just over 10. Is there a further test I can do to find out where the leak is, or if there is one? I understood that I could have a bad seal where the master cylinder meets the booster, but I don't seem to have any fluid leaks. The fitting where the vacuum line meets the booster seemed very clean when I removed it, so I doubt any fluid is being sucked into the lines. Thanks a lot!

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1980 300SD (daily driver), 1981 300D (Inca Red)