Richyb1

ukrkoz

Yellowing outside or inside? Outside, paint shop will buff it for you. Takes literally 5 minutes to do, I witnessed that done.
Otherwise, try CERTIFIT.

mnewxcv

If you are at all handy, do it yourself. There are many many kits on the market. The standard 3M kit is the most well known and been out for years (was one of the first consumer products), however, it is somewhat of a bandaid, and similar to what you would get done at a body shop most likely (sand/cut/polish). It will look great, but it will be temporary.

3M has recently come out with a new version of their headlight restoration kit (be careful when buying, there are about 10 variants). 3M #39175 contains the same components as the older kits (500 grit sanding discs, 800 grit sanding discs, a 3000 grit trizac disc, and drill adapter), but instead of the last step being using a foam cutting pad with rubbing compound to achieve a shiny finish, the new kit has a UV clearcoat application as the final step. The haziness you see currently is a breakdown of the current UV clearcoat, and sanding will remove even more if there is any left, so when you just buff your headlight to a shine, there is no protection for the plastic, and it will fade quickly given strong sun exposure. This is why the UV clearcoat is such an important step.

If you own a power drill (I recommend something 18V or better) you need nothing other than what is included in the kit. Here is a link to the product I am referring to: