I am autocrossing an 04 M3. Amazing fun, even after a 97 M3. However, my co-driver and I have experience loss of brake boost in some various circumstances. Active Autowerke says it's not an uncommon thing. The car is holding vacuum in the booster when parked for days, so the one way valve at the front of the booster is not leaking. Given the very different plumbing for the vacuum source, I am sort of not surprised.

Anyone else experienced this? Any suggestions on remedies? We have adjust our techniques a bit, and that has helped. Just wondering if there is a mechanical "fix".