If you are getting red foam, that would indicate air to me, so while it may take a while for the bubbles to rise and pop, it still sounds like just bleeding is the problem. I'm not sure which one anymore, but at least one BMW I have owned seemingly had to be filled right up to the top not to have a problem like that. It's been so long ago that I had a problem like that with my old Bavaria that I can't remember for sure, but it seems like it took a while before it really settled down. If I recall, you have a 528e, so you are lucky you don't have the power brake booster and cooler line to bleed also! Mike W.