I have used three DV's on the car. A screw together diaphragm type a Bailey single piston and a Bailey twin piston. The twin piston was by far the best of the bunch but still had side effects so it was binned. I've owned my s2 for nearly a decade now and a lot of parts have come and gone as it's evolved.

Nothing to do with broken or unsuited valves, it's totally down to the way KE-Jetronic functions and it's inherrent inability to deal with air leaks in the system (which a DV creates).