Thanks C, ?I don’t recall seeing one like this. Your pic gives me a much better idea about its construction.

I can just make out a line going across, almost thru the center, but I can’t understand why cracked mica ??would “open” the capacitor; but it might short it out. ?

B looks rusty?

The other “plate” is connected to the screw somehow maybe, and then to some kind of terminal? Likely on the nut side?

GUESS? I have not learned much over the years.