I just changed the rear brake pads on my 1979 450SL. I used after market pads, cost $28. Also installed new anti-rattle springs. Brakes work fine but squeal when braking in forward and reverse. Removed pads and coated metal backs with Disc Brake Quiet gunk I purchased at NAPA. Brakes were quiet for a short time then started to squeal again. Removed the pads again, scraped off the old gunk and put on a heavier coat of the same stuff. Brakes again were quiet for awhile then started squealing again. Is there any way to stop this squealing short of replacing pads with Merc. Benz Original equipment pads?