Under no circumstances should grease or oil ever touch the brake pad material. The only substance that should contact the pad surface is brake cleaner. That will not cure your squeel. Mercedes does have a special brake rotor cleaning pads that replace the pads and there is a procedure to use them but I don't know about it.

I had a squeeking problem that was cured by changing the rear pads to OEM. The PO had a chain store change the brakes and it always squeeked. I just changed the front pads and the "thick" pads fit without the backing plate. I used just a little brake paste and they broke in fine, with no squeeks. My suggestion is to replace the pads and check the rotor thickness to be sure you are within the repair specification. Brake in: 50 mph slow brake to 25 MPH. Repeat perhaps 20 times with time to cool between. Good luck.

__________________
Steve
1985 Mercedes 500SL Euro (Gray market)
1995 BMW 520i Euro (Gray market)
1992 BMW 525it Wagon
1994 Honda Del Sol Si