the ONLY correct way to permanently and properly fix a headlamp lenses is to sand it down with a sanding kit, then buff, polish, degreese, claybar, then mask off, and do 2 coats of clear coat, then a wet sand at 2500 grit, then 2 more coats of clear and another sanding, Claybar, then a nice coat of a quality ceramic paint protector
any other is not going to last and will hase up again with time and sun exposure.
^^^^ yes.
I've polished the headlights on a few vehicles, So far, I've been lucky they were the flat style, without the little dribbles, so they were easy to sand down.
The issue is that the top layer of the plastic lens becomes...junk. Most of it is oxidation as UV rays affect the plastic, but some of it is also dirt, grime, sand, bugs, baked on as you drive when the lens is hot from the light.
The bug spray/deet is a cool science trick, but it doesn't work. I guess technically it kinda does, but barely. I remember a shady guy standing out front of Advance Auto holding an unmarked can (bug spray with label torn off) approaching people saying "I'll clean your lights for $10". He even 'gave me a sample' and wiped his rag down the middle of my light... Nice of him to leave me with a streak like that.
2 days later, streak looked the same as it did before.
the bug spray 'melts' off the top layer, but leaves it vulnerable so it oxidized even more rapidly.
I picked up a set of lights for a Tacoma I owned. They weren't badly oxidized in the typical cloudy way, but they had this horizontal dis-colored streak about 2/3 down, where I suppose the heat is most intense. I sanded it down, polished it, and did clear coat. These are a few pictures of the process
Original condition. Got that streak, and some spiderweb pattern in the lens, also kind of an orange peel pattern
This is about half way through. I started very fine steel wool, then 500 grit, 800, 1000, 1500, 2000, 2500.
This is the finished product, before and after. Both lights started in similar condition.