Wish I could help. I too had a gas stain on powdercoat, on my drivers side rear FIA wheel on my Cobra when an A/N fuel line connection from the tank along the frame wasn't tightened down tight enough...it sprayed fuel all over the wheel. I tryed everything I could find and was recommened and nothing worked...cleaned it up somewhat using a mixture of Simple Green and acetone...it still left a lighter colored yellow stain on the wheel. I finally opted to have that wheel re-done.
If anyone has a surefire method I too am interested