Peter Frederick wrote:
Most likely a defective brake booster. It should hold vac indefinitely.
Sometimes the brake booster and master cylinder fail together. What sometimes happens is the M/C rear seal fails and fills the brake booster with brake fluid. The brake fluid eats a hole through the diaphragm and the power assist goes away. Now you've got crummy brakes and you're burning brake fluid in the engine (gas car) or sucking it into the vacuum pump (diesel). Used to be real common on some VWs.
