Regarding the turning of MB rotors....
Look at what MBDoc had to say in this thread:
http://www.peachparts.com/shopforum/showthread.php?threadid=12589
I went thru about 4 bad sets of OEM rotors a few yrs. ago. One right after another. Got sick of spending my weekends replacing rotors. Had the last new set I put on turned. Problem solved.