Hello. In very tldr fashion, my dad had this old respirator from many years ago, never used, and when we took it out of a box to look at, this yellow circle (which I'm assuming is a seal or a diaphragm) crumbled like a thin sheet of dried paint. Does this render the mask unsafe/unusable? If so, is it replaceable, or would it be easier to get a new, modern one? Any information is welcome.