I used to detail cars.....
I cant remember the name of the shit we used but whatever the case, if you use it and it works(which it should) I would advise that you re-apply it every so often to keep the clearness.
From what I was told, the actual cover over the light has some type of oil in it and it dries out over time which is why it turns yellow.......
So sand it real good and you should have some great results once you start juicin it back up.
I think people should do that at least like once a month to keep it lookin new....versus buyin new head lights...and we all know that shit aint cheap!