Seems silly to start a whole new thread for this, but I didn't find anything using search, and didn't want to jack someone headlight thread.
If you have a customer who needs headlight repair but they also have headlights that have water or sweating look on the inside, what can be done? Sanding won't fix the inside.. anyone dealt with this?
Not sure what can be done, other than the obvious, and I'll explain.
I take it that you mean the sweating (moisture intrusion) is there at all times, that it never dries? Has it left staining-spotting?
I was once having such a problem with my Kia Tail Light Assemblies, water getting in them. The assumption was, that water was entering where the Lamps twist into the assemblies, that there's commonly a foam rubber gasket, and that gasket isn't doing a good job of sealing.
The first time, I just removed the assemblies, took a hair drier, dried the moisture out, and re-installed. It came back again shortly after.
I was noticing residual spotting inside, and the second time I decided to go for broke, and take a more aggressive approach. I remove both, took to kitchen sink, a few drops of Dawn, and filled them with warm water. Simply placed my hand over the lamp hole, and shook like mad.
I rinsed thoroughly with warm tap water, shook out as much excess as I could, then rinsed again with a few ounces of distilled water. Drained, and again blow dry the assemblies with the hair dryer.
Then, I got me a little tube of Dielectric Grease, applied a thin coat on the foam gasketing on the Lamp holders, and re-installed. The problem has never come back, and the assemblies are crystal clear in and out.
How such would work on a headlight assembly? Hard to say, since the lenses are clear.
It might work fine, and then again might compromise the reflective coating on the rear of the assembly.
In any case, this is something that really cannot be done with the assemblies on the vehicle, they would have to be removed. It's a very chancy undertaking.
If a blow dryer can be gotten to the rear of the assemblies, one can maybe at least first try drying them out, then as I say, apply a good dielectric grease to the lamp holder gasketing to prevent future moisture intrusion.
Mark