^ Um I would use a different BMW dealer then, that's ridiculous. They know an exhaust isn't the reason your window motor broke or NAV screen died, they're just being assholes. Ask them how a BMW stainless steel 3" pipe is different from a non-BMW stainless steel pipe, hahahaha.
My dealer saw all my parts when I recently took it in for warranty work, no problem. Shit even Mitsu replaced my transfer case under warranty on my Evo 8 with a bunch of parts on it.