I have a 2001 330ci convertible with a defective rollover sensor (PN 67-91-6-918-515). Bought the replacement part from Tischer BMW but can't figure out where it is physically located on the car. I thought it was the unit under the rear seat cushion but that's not it. Anyone know where it is and have any experience replacing it? Your insights would be appreciated. BTW: local BMW dealer wanted near $500 for the sensor, most on-line retailers wanted ~$435, I got it from Tischer BMW (email@example.com) for $365.86 delivered.