bvanderbilt,
Taking no responsibility if you choose to do this, I suggest you get your differential bolt fixed on your dime and take your car home. No claim necessary, the bolt is cheap (
http://realoem.com/bmw/showparts.do?...18&hg=33&fg=05) (33176760343), and the replacement should not take more than 30 mins. You should be out less than $100 and rid of this headache. Once the differential is fixed in place, get your entire rear end checked by an indy shop.