Joined: Aug 2009
Location: Colorado Springs
Read this because it'll take me a second to get to the point:
I cracked a plastic coolant tank on my race quad after crashing one time. The replacement was expensive and had to be ordered. I went to Lowes and bought some Loctite Marine Epoxy. It mixes up gray in color, and dries into substance that is probably just about bullet-proof. It sealed up the crack in the coolant tank and has also proved useful for sealing my Mustang headlights.
So if you don't mind that it's gray, and you don't make a mess of it, I'd recommend using to seal the headlights.
BTW... the stuff is sandable and also works well for filling in the holes in your trunk if you ever do a spoiler-delete.