In my experience with plastic lights, The best way is to Sand them down 320, 500, 800, 1000wet, 3000wet Then simply lacquer them off, Admittedly i work in a bodyshop so i have access to a booth, But the lights come out like new and dont fade off like when polished, The only down side is like paint, If its chipped and your local car wash go at it with a jet wash you will get lacquer peel on the lights, Mine on the white clio have lasted over two years though, Both of these suffered badly with yellow lights.