I just took apart a booster from an 86 735i. It was an ATE brand. The o-rings sizes were differant to the ones posted by James and also contained 2 teflon rings on the large piston. I can find all of the parts except the 9.5 mm id x 22 mm Seal in the nose of the plastic part that holds the spring in. Apperantly that is an odd size and is so far not available.