I'll order ATE rear brake rotors and hardware and compare outside rotor diameters to the Centric 12135002 rotors and the ones removed from the car.

My early W126 uses a dowel pin for rear brake rotor alignment, not a screw as in later versions. The Centric rotors have a loose fit at this dowel pin, so it's possible the rotors aren't centered well and are scraping the anti-rattle clips as a result. Maybe I got what I paid for with $13 brake rotors, or the clips are too long or something.