My wife's Audi's headlights had gotten so yellow and crazed, we were worried about getting a ticket. As a risk-free experiment (since they were toast anyway) I bought a restoration kit made by 3M. It included 3 different grits of abrasive, a buffing pad and compound, all of which fit on a normal hand held electric drill. The results were amazing. The headlights look brand new.
If you have a scratched windscreen or helmet visor, this $16 kit is worth a try. I wouldn't hesitate to try it.
