Have you considered filling the cracks with an optical glue, like Norland? It cures super clear, but I am not sure about the interaction with heat.
BTW, way cool!
I had this thought as well and tried to fill the cracks with a clear silicone, described in one of my later posts above. It seemed to fill the cracks alright, but I still had some areas start to burn. That might have been from some small previously burnt sections that I didn’t remove well enough. There is just a lot of potential edge area to burn. It’s the sort of thing that would need to be perfectly done to work; no flux anywhere and everything perfectly clean.