NavList:

Hi there Gary, I think I have pretty much figured out how the pellicle was damaged. I suspect heat, previous owner must have improperly stored the instrument. Such instrument has a black surface.Exposing under summer sunlight would definitely results excessive heat to be accumulated inside the casing, causing the pellicle to melt and deform.

I was wondering if a piece of heat-resisting transparent plastic sheet or a very thin glass will do the job? I could not find a platic wrap that has a satisfacting smooth surface.