yeah ive heard to use liquid nail. however, mine are just siliconed right now, and are holding up fine (hopefully this trend continues). i was worried about the silicone possibly not being strong enough, but it seems to holding up fine. this is all with
0 fogging.
another thought i had was to use epoxy in a few spots (like 4 or 5 spots around the headlight) for strength and then fill in the crack (where you cut) with silicone. i didnt know how well the silicone would seal to the epoxy though.
not that you would really want to try on someone elses headlights that you are working on for money, but its just a thought. maybe you should get a practice set from the junkyard to practice a new sealing method that yeilds absolutely no fogging before you start selling these. or just use more liquid nail.
for 100+ bucks, i would expect at least that
