Stick piston in the rear caliper -- also the pads got worn down and hit the spring, so that the rotor is worn funny.

Replace rotors and rebuild rear calipers.

Check the bushings on the rear control arms, and check for rustout on both -- W126 rear control arms rusting out is beginning to be a problem. If you replace the, drill a ventilation hole in the bottom and paint the inside.

Peter

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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!