If you have a haze or small scratches the best product I have used is Novus NOVUS Plastic Polish
My back plastic was almost unusable until the dealer had a detailed come in and work on window. He used this and it turned out great. It of course isn't new but close. He only spent about an hour on it and I will work a little on it this spring. The edges are still showing signs of age but just a quick look no one would notice.
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