The only way to clean the headlight is to first remove the decomposed plastic then put on a new coat of protectant.    There are several ways to do this. The easiest is to have a professional come out and clean your headlight lens.The next is to purchase a kit designed for that purpose. Answer   Most Tiburon and other sport car sites should have specific headlight cleaning details, but if you want to clean the inside of the lens, you'll need to r … emove it and either put it in the oven, or apply a heat gun to the seal.