I am helping a friend with an '82 300SD. When I hook up my test gauge on the vacuum booster line I get a fluctuating vacuum signal that bounces between 0 and 4" Hg (negative obviously). Next when I shut the car off and disconnect the vacuum booster line at the brake booster I hear vacuum "escaping". With the line disconnected at the booster and running the engine with my finger over the vacuum hose where it connects to the brake booster gives me around 15" Hg negative (which I feel is "good" vacuum). It seems obvious that the brake booster is leaking pretty badly and I just want someone that has seen brake booster failure verify this conclusion. It looks like it is probably a pia to replace the brake booster because, based on what I can tell, it is bolted up on the cockpit side under the dash (I hate under the dash work). Thoughts/comments are welcome and are brake boosters rebuildable?
thanks

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Jim