We bought my wife a 2008 TT roadster. And it has 19" split rim aloys on it. (was the FD's car at Sheffield Audi) so it looks amazing. BUT, the rim around the edge is showing water mark style corrosion spots. The metal around the rim seems to be made of different metal to the alloy in the middle. It's a different shade definitley. I have been reading that split rims generaly have machine polished rims, but I'm not sure if that means I can just polish the rims back to former glory, or will I need them professionally refinished and coated. Any ides guys?