it's a daily driver, and those rotors are ATE and just over 12 months old. the internals of the park brake were removed when i put the last rotor on (because it had some issues). The caliper was fine, as were the pads. even on both sides, no rotor warp and the wheel bolts didn't seem to have any problems..

from another forum a brake expert seems to think it's from the casting. a cold spot that has popped out

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W114 1969 250CE - M110
W114 1972 280S - M110
W116 1979 450SEL - M117