I have a 1990 chevy truck,and the headlights where turning yellowish
I used some Wenol all purpose metal-polish.
PLUS: Fiberglass, Plexiglass, Tile, Formica, Enamel Surfaces, and much, much more.
http://www.autogeek.net/wenol1.html
I use a product from "The Wax Shop"
LRV Protectant
greaseless conditioner for Leather,Vinal & Rubber
anti-static and no oily build-up
have not found it around here in awhile,and I'm on my last bottle
of it.