Some years ago, I had in my hands a rather sad looking XRR fuel tank and I thought, "what the heck, I cant make it any worse". After checking there were no petrol fumes left (one decade of emptiness did the trick), I (gently) put a butane torch to it and saw the color come back, some of the scratches disappear. With nothing much more to loose, I also tried sanding some of it, with little success but then tank was back to reasonable, shameless, usable condition, yay!