Front Air Bag Sensor Control problems of the 2000 Mercedes Benz ML320

Srs light came on 2006. I called dealer who told me it was likely a failed child sensor in the passenger seat. I was advised the srs was still intact and that these sensors are known to fail [mb 2000 ml 320]. August 2008 dealership advised me that I've had no srs working since the light went on and so I paid $900 to have a $291 part replaced - $700 in labor. My complaint is that a safety feature light warning like the srs - and a failed sensor - needs to be a manufacturers responsibility.