If you look at the face of the piston, right here:
http://img.eautopartscatalog.com/live/N1040110891ATE.JPG
you will see 2 distinct marks at about 12'o clock and 4'o clock position.
Have a look at your calipers & see if the raised portion of the piston is anywhere near a 20 degree angle.
In my experience, I would opt for brake discs from the MB dealer, or buy Zimmerman.
