My rear pads only lasted 15,000 on my 00 ML430. I needed both rotors and Pads for a cost of $538. I couldn't believe it!!!
When I complained, I was told that I was lucky (service manager claimed he only gets about 12,000 miiles) It was furthur explained to me that all sophisticated users know that you only get about 12k to 15K miles on a set of brakes. I was also told that it is normal for the rear breaks to wear down to the metal without ever activating a sensor. How convient since this means MB get to replace both rotors and pads. It should also be noted that the rears need replacing about twice as often as the fronts.