Pump the brakes up with the wheel off the ground, then open the bleeder valve and see if the brakes release. If they do, replace all four brake hoses (both fronts, both rears). The lining inside can separate from the outer cover and act as a one-way valve -- pressure goes to the caliper, but nothing can go back, so the pads drag, and the hotter they get, the more they drag.
Check the rubber on the dust boot behind the pads -- if it is cracked or brittle, you need to rebuild the caliper, it will stick otherwise.
The dragging brake scenario can also be a result of running new pads on worn out rotors -- if the backing plate on the pads is touching the anit-rattle spring, you need new pads and rotors, the rotors are seriously under thickenss. The causes the pad to hit the spring, and it cocks up on the bottom. This will cause the piston to cock int eh bore, and stick -- roasted brakes.
All my old benzes (and my brother's 300D) were in this condition when purchased.
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!