Plastic polish There are number of products on the market that will polish plastic, this may be what you want. BavAuto, Griot's Garage (though usually higher in price), plus the local off-the-shelf brands offer them. I don't have any personal experience with them so I can't recommend one over the other. Maybe try the detailing forum? Good luck,
You can restore some or much of the original look of your headlight covers with headlight cleaning kits, with rubbing compound, or with sandpaper (600-1000 grit and finer). Plan to invest a lot of time, not just a half hour per headlight.You may want to remove the covers so you're not rubbing down the car's paint at the same time. Good luck.
We have used Novus plastic cleaner with moderate results. It is a three step process with different liquids that I learned about from a person who repairs pinball games. It probably is not as thorough as hitting them with sand paper, but you also won't damage your paint and is readily availabe at auto parts stores.
I say forget cleaning... at 8 years old there will be a slight film on the inside of the plastic cover and a more significant film on your round glass lenses. Purchase new plastic headlight covers and gaskets, disassemble the headlights, swap the glass lenses over to the new ones and it will look much better. OEM BMW Hella is a bit pricey, you can go DEPO as I did and they are ok in quality. A guy on Ebay recently had the OEM euro clear corner ones for $200 - good price.
