I don't think there are too many aftermarket discs out there, jut OEM.

You must pull the hub on the W126, and unbolt the rotor from the rear. This means repacking the wheel bearings. Be carefull when adjusting them -- the "factory" drill is to measure the free play with a dial indicator, but you can get close by tightening the lock nut until you feel significant turning resistance then back off 1/3 turn and tighten the lock screw. Slightly loose is better than too tight, the races will spall and chew the bearings up if they are too tight.

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!