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I haven't done the ones on the Porsche, but I did the ones on the Firehawk (more open wheels) over a year ago and it's still holding up fine (have even been through a couple of track days).
I once painted my rotor hubs with that color changing temperature sensitive paint. They changed color according to the highest temperature they reached. The can of paint came with a chart for color vs. temperature. I don't remember them rusting, but I do remember them turning the color that was 850°F.