Hi roland,
Yes, I can see the "solidification" but the picture is not well exposed. What it looks like is peeling or curling of the LCD polarizer on the front of the LCD panel. Have you taken the watch apart yet? Have you felt the face of the polarizer? If not, I suggest you do so to get the exact diagnosis.
If it is indeed the peeling of the front LCD polarizer, you could try removing it with a razor blade, but it is difficult. Once the polarizer is off, you would want to get a non-sticking "high-contrast" polarizer film and place it in front of the LCD panel. The only other alternative would be to buy a new LCD panel, and install it.
This may have been caused by humidity if the owner at one time lived in a part of the world where there was high humidity. Try taking the watch apart, and making sure of what is going on with the LCD panel first. I do not think it has anything to do with the rear reflecting mirror.
Thank you,
- Patrick