I just fixed the same problem on my Lexus and used Meguiar's PlastX. It is a clear plastic cleaner and polish; in a nut shell, it restored them better than new. It was very easy to use and did both front headlight lenses in 5 minutes. It worked so good that although they are red, I did the rear lenses too.
http://www.meguiars.com/?clear-plast...Cleaner-Polish