I can't see how a catted dp can cause this issue, does not add up to me. Motor sounds like it was factory defective. There is a thread on these motors having mysterious coolant leaks.
They will have to prove that dp caused the issue before they just claim it's the fault of the dp. To me it does not make sense. It is a very popular mod . Don't let them easily convince you your at fault for something that was probably and more likely a factory defect. Sounds like a defective head gasket issue for sure.
Please review this thread especially the last few pages
http://f30.bimmerpost.com/forums/sho....php?t=1292652