Hi
Did anyone ever find the solution to this?
What is actually happening is the loss of the stored vacuum in the brake servo. When the engine is switched off, the servo should be able to hold a "reserve" amount of vacuum for emergency use. This usually equals 3 full pressure activations before the reserve is extinguished. The vacuum is held by a non-return valve, either on the servo itself, on the inlet manifold (or diesel vacuum pump), or anywhere along the vacuum line.
There may be a weak point somewhere along the line, or in the non-return valve. I do know that VW and Audi often have to make quite difficult engineering decisions - obviously, they are all initially designed as left-hand drive, and then bits like steering wheel, pedals, and brake master cylinder and servo have to be swapped over. Indeed, my S4 has a completely different designed servo to the LHD models. Maybe they don't quite give it their best effort, just for us Brits, eh!
One other cause for loss of vacuum reserve - you don't happen to let young children sit in your car at home, "playing" driving like "daddy", and pumping the brake pedal!!!
