Hey j930...really sorry to hear that you're going through this and have already spent some $$ to no fix. Hopefully I can help out a bit...I've included a link to our tech articles on the 3-Series brakes. Feel free to browse and see if anything is relevant and can help you further diagnose the issue. If you have anymore questions, feel free to post a Comment just underneath one of the articles and someone will get back to you with technical help. Best of luck!
BMW 3-Series Brakes Tech Articles -
BMW 3-Series E90 (2006-2013) Technical Articles - Pelican Parts
-Dmitry