[drh4683]

in rare cases do you need to dissassemble a 21FJ. Reason being, the rubber gasket can break down and cause an oily vapor which adheres to the inside of the glass. I had this on zenith. The gasket was in good shape, but was "tacky" and oily to the touch. After good cleaning of glass and the gasket, it should be many years before I see the problem like this again.
In the pics below are the before and after photos. Obviously the problem is no where near as bad as cataracts. The darker ring around the crt is the oily residue. What the photo doesnt show is the thin oily residue that was covering the entire surface area of the crt and lens. This defocused the picture pretty bad. Best way to describe it, like bringing the set in a warm room after being out in the cold, condensation forms on the crt .
When I found this set, it was in a clean attic, however being in an attic it gets VERY HOT in the summer and baked up there vaporizing the gasket composition.