I normally don't have to clean 9 years of brake dust off the inside of a wheel, I used anything I could get my hands on. I was even going to post looking for ideas. I ended up using several types of the brake cleaners found at automotive stores, then a lot of dawn, power washer, then some 3000 grit sand paper, I figured they couldn't get any worse. In the end they came out ok, maybe a 3 on a scale of 10 in the Porsche wheel world
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I'm looking for ideas if I run into any more like this. I know when I got my Boxster which is two years older it was pretty bad two. I used pretty much the same process and they are decent too.