Meguiar's Direct Plastx ftw
 

My 2003 coupe's headlights outer layers were almost yellow after 7 years .so when i was looking at the car magazine and saw the plastx i thought i should give them a try. its around 15-17 bucks, it comes up with microfiber towel and an applicator pad you can use with a auto-drill. all you do is put the liquid gel in use the pad and wipe off with the cloth. The results were amazing (i was so excited i forgot to take pics, i ll try to get some old pics and show the difference) my headlights look like brand new :) definitely a good cheap solution for old contaminated,oxided headlights. they do have the kit in crappy tire.

Thats great. Its also a good idea to put some sealant on them now, for UV protection.