It sounds like what you have is a broken (snapped & shredded) seat motor drive cable. There are 2 for ea. motor, one for ea. side. On my `88 M6, this is the rear-most motor. You will need to order a replacement through your favorite dealer. If it's like mine, it's the 220 mm. cable. Mine hase seat memory which uses the shorter cable. If it's NOT like mine, you wil PROBABLY need the 230 mm. cable, listed in the fische. My experience has been that they have to come from Switzerland, so it will take over 3 weeks. In the menatime, don't be moving that seat back or you'll do worse damage, like bust a gear box -~$200+ !!