Gilly and DR.DIESEL,
Don't these cars have a system to "dry" the pads and rotors by applying the brakes lightly when they detect wetness? I am not sure how this system works, or if it can work with only the rear pads, but if it is malfunctioning, I guess nearly anything is possible. In any case, I would think the car's performance would be suffering if you were driving around with the brakes lightly applied all the time.
If you put the car in neutral and let it coast after getting up some speed, does the car coast or does it slow down a little faster than you would expect?
I agree you need to find out what the problem is, and I do not think it is confined to needing new pads. Good luck, Jim
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)