The white is molded into the tire as white rubber, if the oils are seeping through from the back, how does cleaning or sanding the surface help? If only the tops are staining, the oils in the tread cap are in fact leaching into the white casing. Just get them replaced and get some free new tires. Burn rubber all the way to the dealer....even if your not the original owner, its a BFG issue, not a dealer issue. They can just write you off to BFG recall and they get it all back
