It looks like it was the item labeled #7 in this post - the "Adjuster Unit". The local dealer had 5 in stock, told my guys they go out a lot. $306 for the part, but it looks pretty easy to replace yourself and I'm sure you could get the part cheaper.

http://www.xoutpost.com/x5-e53-forum/...tml#post565171

Just drove 30 miles back to the office, no problems so far. Going to have to relearn how to drive without the code reader plugged in.