Just an update (not a happy one!). The car was back at the dealer yesterday. Got it today. He said he changed the pads (again) - complained about how mercedes changes the materials in their OE pads without informing them. Well, the squealing has not gone away at all!
Once the brakes are hot, they SQUEAL, LOUDLY, always at low speeds, sometimes even at less than 5mph (when just coming to a stop).
Am taking it back again on monday. Very frustrated!!! Please help with ideas if you can. I didn't make the common errors - went to a dealer so that I get OE pads and rotors, got the pads and rotors changed TOGETHER, and I still have crappy brakes!!
And just to mention it again - my brakes NEVER squealed before.