One thing I would like to suggest, which is extremly odd but did happen to me is that the small seal that goes between the master cylinder and the power brake booster failed. I thought the engine was failing because I was getting clouds of smoke out of the tail pipe-intermittently. My '68 108 250SE has a small plastic "trap" between the intake manifold and the booster in the vacuum line. It had fluid in it, which I found out was brake fluid. Evidently the seal had started to fail, allowing intake manifold vacuum access to the back of the master cylinder where the actuating rod pushes on the cylinder's piston. I guess when the throttle plate closed when slowing down during driving, the manifold vacuum was high enough that it would pull fluid out of the master cylinder. Every once in a while a slug of fluid would get pulled into the engine from the trap, which was filled with brake fluid. A cloud of smoke would come out of the tailpipe. the really strange thing was that I had just replaced nearly all of the brake components thinking I had a small leak somewhere-which I could never find-and that was why it was using brake fluid. I had never heard of such a thing in the 30-odd years that I have been working on cars, previous to this situation.