My ML has 50k miles and, I'm told, needs brake work. As yet, no brake warning has shown up via the indicator lights but a couple of people have suggested that the pads are "thin". There is a question as to whether, when I replace the pads, do I also need to replace the rotors. In looking through the various posts here I still do not find a definitive answer.

Here are my questions, 1.) Should I go ahead and do any work at all or wait until the indicator light shows up? In other words is the indicator light reliable? 2.) Is it important to replace the rotors when I replace the pads? For clarification, the rear rotors have a ridge that can be felt around the outer edge of the rotors. The front do not.

Thanks in advance for your suggestions...........

Rotor with the ridge more than likely needs replacement. The other might be ok, but both need to be 'miked' for thickness. Rotors are so inexpensive for the ML...I would be tempted to replace rotors and pads and be done with it.
DIY and save big bucks on both discounted parts (not list, like shops charge) and of course labor. Lots of good info on this site for changing out rotors/pads......

The rotors will have a number stamped on them that gives the min. wear limit. For front 23 mm for rear 13 mm When a rotor gets within .5 mm of each of those numbers it is supposed to be replaced.