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).Google+
Car Problem Reports
Mercedes-Benz 300TE 4MATIC Replace Brake Rotors When Pads are Worn and Squeaking
Mercedes-Benz 300TE 4MATIC Problem
Visitor, 1990 Mercedes-Benz 300TE 4MATIC, 250,000 mi
I think all of the 300te wagons form this brake lip. The rotors must be replaced when this occurs.