I Have a white-light metal on glass solar filter made by Thousand Oaks, which I acquired for the 1999 eclipse.
Inspection still reveals no pinholes or scratches (it has always been kept in a padded case) so my only concern is if these kind of filters have a known lifespan before they allow too much light to pass, especially in the IR & UV.
Visually, the image seems no brighter than it was 22 years ago, as I still use it with the same 90mm Mak that I bought it for, although memory is a funny thing with humans!
Does anyone have any knowledge on this subject. Thanks…