I also have Zimmerman rotors.
My theory on the commonality is that we don't drive our cars every day. My theory is that the rotors get slightly rusty from rain / humidity, but not in the spot where the pads are resting on the rotors. Driving scrapes the rust off off the rest, but the rotor is never the same from that point forward.
Should I do an experiment where I remove my brake pads every time I park the car?
