Rotor thickness is critical on a Benz. MB uses thin rotors to reduce unsprung weight, and this means that there isn't anywhere near as much "meat" there as there is on most other cars. They don't warp, but they do need to be replaced every other or every third pad replacement.
There is a minimum thickness stamped into all OEM rotors on the circumfrence, but this may be hard to read and won't be present on off brands anyway. The quick and easy way to tell if you need new rotors is to check for a disctinct lip on the outer edge, where the pads down quite cover, and at the center beyond the pad area. If there is a lip, or the friction area is worn down the the base at the center, don't bother to measure, replace. They are very inexpensive.
You will discover if you try that they will be too thin if you turn them.
Front rotors on models before the W201/W124 chassis are bolted to the hub from the back, so the hub must come off to repalce. Later models are held on by the lug bolts.
Clean the bad slots in the calipers carefully, crud here can cause squeals and sticking brakes. Use on OEM pads, and put anti-sieze on the back of the pad where the piston contacts the pad and the sides of the backing plate were it contacts the caliper to prevent squealing.
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!