You can't rebuild some BMW gearboxes because the parts are not available. I have an E39 that will need the tranny replaced eventually. I went to several reputable tranny places and BMW does not sell the parts to rebuild it. You are stuck with a new BMW tranny or a used tranny. When it is time to replace my tranny, I will opt for the brand new, since I plan to keep my car for awhile. Good luck.