Corona dope? No, I am
not calling names
...
General cement made/or makes a thick gooey black paint (in a small bottle with an applicator brush) that is painted over the problem areas. This may still be the "product of choice" for these problems... don't know... people might be using RTV or something else these days.
jr
Update: Looks like the stuff is still available... even listed on Amazon (with awful shipping charges):
http://www.amazon.com/GC-Electronics.../dp/B000B62YO8
Likely it can be found cheaper elsewhere.