PlastX works good, but don't forget that it's a cleaner/polish, it leaves no protection behind so unless you clearcoat/seal/wax the clear plastic afterwards, it'll oxidize again quickly.
I use Plast-X and it works great. I used Meguiar's G17110 Headlight Protectant to seal it. I think it is the same stuff discussed here, that was renamed. I bought it five years ago. You do need the protectant after the Plast-X. It is very thick not water/milky like 303 Aerospace. The stuff must work because I still have the bottle from five yesrs ago more than half full.