The spring seat...In My '97 540 it was very weak, It cracked on me while in the middle of something very important. The stealer didn't want to sell it to me seperately so I had to buy 2 Front Shocks brand new.. Which is useless because I have Bilstein Sport shocks all the way around and just needed that one piece. The whole passenger side dropped, I puntured my tire and the spare in the trunk just to get me home...Every 5 series driver should look into checking this out... GREAT HEADS UP ROOZ!!!!!!!!!!!