OK, i went to the dealership today (for foglights, damm there expensive). I asked the guy there about the seat motor for the Z3, it turns out theres 2 motors, one at the front one at the back. Each one controls differnt seat functions. Sadly an OEM motor will run about $150-200. The guy said there is a slight chance that a motor from a 328 would work, but youd have to check the part numbers on em to see.