How do you know the oil was always changed at the dealer and a reputable indie? I'd almost bet money it was one of those quick lube places, or a previous owner, that did it. I trust the work of BMW dealers around here, I just don't use them because they're too expensive. A good indie has diagnostic tools that I don't, and probably never will. I'm fortunate to be good friends with someone who works at one, so I trust them completely.