Sounds like a line of s***. Dust on the pads has no effect on the ABS system. The ABS system uses magnetic pickups on the rotors to sense wheel motion. I would suspect that the problem is related to the pickups somehow.
I cant understand the statement "don't bleed the brakes on Mercedes unless you absolutely have to". However, the pedal firmness should not be any different before and after the new pads assuming that there was no air in the brake system to start with. It is not resonable to expect the pedal to more firm after a brake job assuming everything was working OK before and you just needed new pads.
I dont understand why the dealer would think that the problem will just go away with time. The ABS system is not sensitive to the condition of the pads or how well they contact the rotors. ABS only reacts to the slippage of one or more wheels in relation to the others.
Personally I dont buy what these people are telling you.
I got too many cars!! Insurance eats me alive. Dave
78 Corvette Stingray - 3k
82 242 Turbo Volvo - Manual - 270k
86 300e 5 speed manual - 210k
87 420sel - 240k
89 560sl - 78k
91 420sel - 205k
91 560sel - 85k
94 GMC Suburban - 90k
97 Harley Davidson Heritage Softail - 25k
00 GMC Silverado 1 ton 30k