Disk brake rotors are mfg'd to some of the tightest specs on any brand of vehicle, esp. MB, down to 10 thousandths of an inch, both in thickness, as well as whether the braking surface is square to the centerline of the bearing.

Regarding surface machining of rotors, American rotors are machined from cast iron castings in three steps: roughing (1st 20-50 thouths), finishing (down to 3-10 thsds) and a final grinding by a 3-4' dia very precise grinding wheel that brings the specs to sub-one thousandths.

When you get your rotors "turned", whether at MB or American dealer or independent, you are barely getting the precision of the second step, since field level machines and setup are by nature imprecise. More importantly you are entirely skipping the final very precise grinding operation that comes in at 10's of thosandths of an inch precision.

The pulsation is usually due to a condition that occurs as rotors wear, usually termed "tri-lobe", because the bad wear occurs as three high and low points. On a 360 degree measurement graphic, it appears as three lumps or lobes. This condition can actually occur at the factory during machining, if hard castings are machined or if the machining tooling wears in a number of ways.

However, what separates the MB or BMW from "normal" rotors, is their much higher hardness, such as in Rockwell Hardness. Soft cast iron might have RH of 80-90, where the MB, BMW (Lexus, Jag, new Cads?) have 110-120 Rockwell Hardness, resulting in a rotor much more resistant to wear and able to absorb more abuse, while returning high braking levels.

MB rotors are designed for running at 155mph/300kph and so the factory specs are going to disallow field level turning to a much poorer quality of configuration.

But, I always go by the feel of the brakes- pulsing pedal? Then they are warped/worn. Get them turned asap, as long as not below min thickness.

Do not use non-OEM pads that are actually a little soft compared to a Midas or other after market. They are designed to fit the system, match the rotor hardness, and wear-in smoothly.

My brother in law simply installs brand new pads yearly, regardless of condition, which is as close as you will get to the factory grinding operation, while you are running and using the brakes.