I recently replaced the tortion bar bushings, and had to detatch the master cylinder and brake booster and move it forward (while still attached to brake lines) in order to access the bushing. When I put it back together, my brakes were terrible. When shutting off the car, I heard a vacuum leak from junction between master cylinder and booster. I loosened nuts, cleaned, put silicone grease on "O"ring, and reassembled. Then, the car would shut off ok, but I would still have brake problems...intermittently no power assist.

I noticed that the "O" ring was a standard round "O" ring, and did not appear thick enough to provide good seal. I ordered a new "O"ring, and replaced the old one. The new one was different....rather than having a round cross section, the new one was square and a little thicker. After installing new seal, I have not had any problem whatsoever.

So, you might be getting leakage through this seal. $2.50 at dealer, easy to replace without detaching brake lines...just pull master cylinder forward enough to get clearance....make sure both mating surfaces are clean. Put a little silicone grease on seal to help it seal.

good luck,

Mark

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1984 300TD Wagon, 407,800 mi (current daily driver)
1985 300DT Sedan, 330,000 mi (gone to that great autobahn in the sky)