I have noticed that many of the cars on the road have inadequate head lites and this is being caused by cloudy headlight lenses. Since 1990 many cars have polycarbonate lenses. This is a clear plastic that will survive an impact, better then glass, as it bounces back upon impact. The problem with polycarbonate is it will yellow and cloud from UV exposure. A number of products are available to repair this haze. All the products work pretty much the same not unlike using rubbing compound on paint. Clean it and then polish. Depending upon the severity it can take several minutes to under a half hour and with the cost of replacement it is time well spent. A drill is almost a necessity, there are claims it can be done by hand by some manufactures, but I doubt this. I have heard of using rubbing compound and polish for the same results but I have not tried it and I would not suggest it.If the assembly has a leak IE crack or hole and has corroded on the inside it will require replacement I would recommend used, and after the clunker program, I have read there are a ton of used body parts. FYI Mequirs has a plastic polish that will work if the lenses are not too bad. I have used it to just clean up lenses both tail, park and headlamp. It really puts a nice finishing touch on a cleanup actually it is amazing what it does to make a car look sharp. It will also work on bug deflectors. Turtle wax has a new product that is wax and a light rubbing compound that works great with very few swirls.