Due to the size and material used on the brakes of these vehicles, the brakes may start to squeak around the 50 percent wear point. The brake rotor surfaces become uneven, causing a lip to form at the outer edge of the rotor. Because of this, the rotors are usually replaced when the pads are worn (pad life varies depending on driving style and terrain).
Car Problem Reports
Mercedes-Benz S430 Replace Brake Rotors When Pads are Worn and Squeaking
Mercedes-Benz S430 Problem
Visitor, 2002 Mercedes-Benz S430
Breaks always squeal. Replaced pads many times.
I replace the rotors every other brake pad change.