2001 Mustang headlight issue

That's interesting. My daughters 2001 headlights are turning to shit. My 99 headlights are still in great shape. I suspect whoever got the contract to supply them in 2001 didn't use very good materials. Only real option if you want them to put out full light output is to replace them.

there are detail shops that can wet sand then reseal for about $50 a lens. We do it here at my shop for $100 set.

The haze is on the outside in 90% of the lenses.

I was told AFTER i replaced my headlamps that brake fluid can be used to clean the buildup inside. however, i have not had to try it since i was told AFTER i replaced my lamps. also, mine are glass. its not an uncommon problem. the sun and the head from the bulb back the inside of headlamps. especially here in florida.

There is no way you will ever make them as clear as they are when new. I'm just guessing based on my own experience but I'd bet when you finish wet sanding them they only put out about 85% of the light that new lenses would put out. And from what I heard, which could be wrong, there is a outer layer of UV resistant material on the lenses that you are sanding off so they will not hold up nearly as long as a new set would (which isn't saying much). The only real long term solution, if you want to see at night with headlights that start out piss poor anyway, is to replace them.