Back in the day, when repro headlights and such were expensive, i had to go this route. I used 100% silicone, not some cheap blend. I used clear. I would take the lense off and put a bead down. push them together and put a bead on the outside joint, then smooth it out with my finger. didn't look too bad. btw while you have them off, if they are not real clear anymore, wet sand them with a fine grit like 1500 or something then buff them out. they will look much better and clear>