I've had 2 sets of front rotors on my '92 Bonneville since 2000 and the noticed that the front pasenger side rotor seems to always develope a groove almost exactly in the same location on both sides exactly in the mid point - even after the brake pads are changed.

That groove, like I mentioned, is located exactly in the mid point between the center andouter edge of the rotor. I've had the caliber checked a few years ago and there'* no leaks or damage, and the open and close normally and the pads wear normally on both sides...

It almost looks as if a stone was caught on both sides of the pads and just etched out a slight grove on both sides over time. Can't figure it out.