Old PlastX eats headlight clear coat?

We have a 1998 Accord which has spent most of its life in a nice cool garage, unfortunately for the last 3 years it has had to sit out in the sun. The headlights are not at all discolored and up until today I had never noticed any defects.

So, today I washed the car. Nothing special, just a capful of some generic car wash solution and a bucket of water. Afterwords again I didn`t notice anything odd about the headlights.

I had a bottle of PlastX which I have been using for years. Shook it up and did the tail lights. It was slightly thicker than I remembered, but it still acted normally, it spread evenly from a slightly damp foam pad, after drying briefly the excess wiped off and polished with a blue shop cloth. No problems.

Then for the first time with this car I thought, why not do the head lights? I had used this product, from this very same bottle, on headlights on a couple of different cars before with no issues.

Not this time though. When it wiped on it immediately became thick, almost gummy. Realizing that wasn`t right I tried to wipe it off again immediately and some came off but the rest sort of smeared. Ran and over wet down some shop towels with a lot of water and tried to rub it off without much success. Eventually the mess dried and I could scrape off the excess with a fingernail while using a very soft toothbrush to brush the powder off. When it was done I could feel a big hole in the clear coat of the lens, it was missing in about a 1-2" tall swath horizontally over large sections of both headlights. Most of the mess had piled up at the edge of this hole (in retrospect), with little islands of materal here and there on the inside which came off relatively easily. I`m sure the headlights were not like that before. I`m not sure I can photograph that hole successfully - there is no color contrast to work with, but it is easy feel the step down and then the step back up going across it.

What the heck happened? Have any of you ever seen this before? I did notice that when I shook the bottle there wasn`t much motion, like it was mostly emptly, but whatever was in there should have mixed. It acted a lot like I had just poured a really strong solvent on the headlight. Near as I can tell the PlastX started dissolving the clear coat on the lenses pretty much as soon as it hit, mixing with it, and forming that gummy consistency. Now maybe there was some damage to the clear coat prior to this which I could not see, but I`m telling you, these headlights did not have any obvious damage prior to this. I didn`t inspect them with a microscope or anything, but I did dry them a few minutes before with my face maybe a foot away, and noticed nothing but smooth even surface.

I think you are on the right path, the product separated and what you applied was probably mostly solvent, which ate into the lens material.

That`s what I was thinking too. The issue then is that somehow or other the product had entered a state where shaking it didn`t mix it well. I think maybe the solids sank to the bottom and over the years, and with the heat (LA garages get really hot...), baked into one big slug. The solvent separated and stayed on top. Shaking the normal amount dissolved a little of the slug, yet it felt like an almost empty container because it was just this little bit moving. When poured out it looked more or less normal because of the small amount of the slug that had dissolved, but it wasn`t, it was mostly solvent.