Unless warped or you had a bad caliper the rotor should be OK at 12,000 miles. You can put a dial indicator against the side of the rotor and spin it to see if it is warped. Alternately you can put a pensil through a piece of wood against it and it should not move when the wheel is turned. I used to true spoked wheels with a pencil. Nail a 2x4 to each side of a wide enough piece of wood to accept the hub. On the top of the 2x4s cut a V for the axle to rest in. Drill a hole in one of the 2x4s for the pencil so the tip would touch the rotor. Spin the wheel and if the pencil moves the rotor os warped.

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