black brake fluid just sounds wrong to begin with!
Flush that out and put some ATE SL or ATE 200 or ATE BLUE brake fluid in there.
All brake pads make dust thats how they work. Mercedes brake pads (OE) textar, jurid, etc, they have a lot of graphite in them which makes the dust look very dark grey.
Other manufacturers make brake pads with less dust because the dust is a lighter color, you just dont see it as easily as OE pads.
For a disc to look blue I would think that it would have to get super hot, maybe a caliper was sticking, but not both, thats highly unlikely.
I am doing a group buy on porterfield pads, which are claimed to be rotor friendly, but with those rotors in that conditon you should get new rotors.
I just thought of something I bet that your master cylinder is stuck. If both fronts are glazed, then the front part of the master cylinder is probably locked up.
If thats the case, you should replace it.
No Benzes in the stable at the moment, but itching for one again.
Former Mercedes in the Stable:
1983 300CD Turbo diesel 515k mi sold
1984 300CD Turbo Diesel 150 k mi sold
1982 300D Turbo Diesel 225 sold
1987 300D Turbo Diesel 255k mi sold
1988 300 CE AMG Hammer 15k mi sold
1986 300E Amg Hammer 88k mi sold
1992 500E 156k mi sold