I just went through needing to cleanup my lenses as they looked like they were literally painted over with yellow paint. Up here in the north (Ohio) our winters get interesting with plenty of days of salt on the road which really speeds up the process of damaging these lenses.
Anyways, 3M makes a white paste rubbing compound in a small pouch that runs around $4.00 that did the trick with a clean cloth. Most auto stores or hardware store will have this. I spent about 15 minutes per light. Applied a small amount and worked it in with a old rag. Before its starts to dry I began buffing it out with a clean cloth. Repeated 2 to 3 times each side and the lenses are like new. I did see a quick temporary fix is using WD-40 applied on each light which works for a good 24 hours if your just in need of that trip in the night and want some extra visibility.