My Audi 90SV6Quattro 1993brakes do not work or at least the brake assist does not work until the car has been driven a couple of miles. Today there is no brake assist even after driving the car further. What is this likely to be and how expensive would the parts and labor be. How can I tell if this is the servo or if there is just a leak? Also the clutch on the air con keeps clicking in and out when the air con is off

 

There might be a leak in the vacuum booster. There is a hose off the intake, that goes to the booster. It can partially fall out, or just get holes in it. check that first.