On Sun, 16 Jul 2017 20:40:23 -0400, Frank wrote:

Problem is not just oxidation but erosion by particulates like sand.

I read all the pages I referenced where I find it hard to believe the
lenses were 'sandblasted'. These look "foggy" and "yellowed" and "cloudy"
but they're not sandblasted, and, for passenger vehicles in suburbia, I
can't fathom the 'erosion' argument.

Of course, in farm country of the dust bowl, I can see that, but then the
paint would be just as eroded, and maybe even more, which is not the case.

So I think this is only "sun" erosion, whether that's a chemical change in
the plastic (oxidation?) or if it's a physical effect (UV damage) I don't
know.

You can polish back with tooth paste but the kit might contain an
ingredient that also makes the lens scratch resistant.

The argument I saw essentially suggested "waxing" the lenses to protect
them from future sun damage, which makes sense only if the wax actually
works, since this is a see-through surface.

I don't see why anyone would want "scratch resistance" in a headlight which
isn't exposed to scratching in normal use (dust bowl in Kansas might be
different but this is suburbia).

I know of
commercial acrylic materials that do this and I suspect some lens
manufactures use them and some don't.

Here's my gut feeling (which can be completely wrong - so that's why I
ask):

1. I don't think it's sandblasting that did it - I think it was the sun.
2. I don't know if it's a physical change or a chemical change (or both).
3. I suspect if there was a "sealant", Toyota would have used it.
4. I suspect, as stated, polishing is the way to go (but I'm unsure).
5. I don't know if liquid "de-oxidizers" (whatever that means) work.

My leaning is toward a 1000 to 2000 grit wet abrasive plus wax when done,
but I don't know how long it will last nor how good it can get yet.