I remember, when I told the car salesman in American Fork after I told him I wanted to buy his used car, that I wanted the headlights cleaned. The car was almost eight years old and the plastic headlight covers were oxidized and clouded. I had other requests--nothing too major--but using some chemical to clear away the film on the headlights is a small price to pay to help sell the car.
Fast forward six weeks. It was a snowy night and I had to go to the local Smith's Marketplace to pick up a Christmas gift for our team's office party. On the way back, a poor deer jumped in front of my car and I hit it. The car slammed into the deer and sent it flying. Thankfully the deer died quickly. The entire front right of my car was destroyed.
The shop that repaired the car did a fantastic job, and, of course, they replaced the shattered headlight cover. The cover on the left side was not damaged, and therefore, was not replaced. I noticed right away that whatever the car salesman used to clean off the cover was wearing off. Soon, the headlight was cloudy and the beam from the light was noticeably weaker than the other, so much so, I think it was a safety issue.
Today we bought a product at Target that claims to clean headlight covers. I followed the instructions and the stuff works pretty good. It's not 100% clear and I guess time will tell if it continues to work.