Replacing Mica Caps

[Winky Dink]

I know that conventional wisdom is that mica caps rarely need replacement, but I've come across several in recent months which positively read fifty percent--or more--higher than they're supposed to. And I also sometimes break off the leads. When I do replace these, what should I use? I've been using 630V polystyrene and 500V silver mica caps--whichever gets me closed to the desired value. Any better suggestions?

Thanks,
Henry