Foam/Gasket Deterioration 

The foam mirror pads in cameras from the 1970s are now turning to dust or goo. You can replace them with authentic black foam, - but where to get it;  It's amazing what you may find in Wal-Mart's, Craft stores, etc. that may work! And, what about that mouse pad next to your computer keyboard?! Another possible substitute is the pads sold for use on eyeglass frames; they may be a light colour rather than black, but this should not be a problem since mirror pads are not in the light path when taking a picture.