Seems like the warranty is completly worthless for this repair. Retail at a parts store the sensor is about $50 and takes not more than 30 mintues to install which includes scanning the stored codes. At that rate they were making $200 per hour labor and 200-300% mark up over their cost on the part. If they make a claim on the warrenty they have even done better. You might have been able to get it done cheaper by an independent MB service guy for less than the what you paid under warranty.