Replace any iffy rotors, it's probably less expensive even in the short run. On the W124, you don't have to pull the hub, either, there is just a conical head screw holding the rotor on after you remove the wheel.

Rears are usually a bear to get off, they've been installed forever and rust into place badly.

Clean the new one properly before installing, no grease on the brake pads, please....

New pads, too, and check the dust boot on the caliper for damage.

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!