A few observations. The gasket on the front of the lamp assembly apparently forms a seal against the opposing metal gasket at the rear of the prism. Two screws hold the gasket surfaces firmly in place, sealing the assembly and making the airspace within rather immune to its environmental surroundings. The letters PPS are stamped on the front of my lamp housing gasket, leading me to believe the substance could be made of polyphenylene sulfide, a high temperature engineering plastic, also known as Ryton. PPS is a plastic that is used in high temperature environments, such as automotive parts under the hood, electronic parts where heat is present, etc. Something has been added to the formulation to give the part its black color. It is possible the PPS, or more likely, the black colorant material could be contributing to the recurring formation of the haze upon the prism glass coating.
Are Eleven Channels Really Enough?