Steve wrote:
I'll second what Frank suggests about replacing ALL of the black
beauty caps. I'm doing that now on the SP-600 I'm restoring.
While none were a dead short, most showed some leakage,
about 100K ohms. In many circuits, that won't cause a problem
but in some its a big deal. About 1/3 had cracked cases.

Steve

Ditto on the Black Beauties, especially the ones with the little brass
tube, they seem to leak like crazy. More on the average than wax
capacitors many decades older.

Also bad news are those pea-green molded caps with the color bands.
Many Trans-Oceanics have around two dozen of those, all leaky.

I havent seen any major problem with postage-stamp or dipped
silver-micas, maybe it was just one manufacturer's kind that is getting
flaky? There is the problem of the silver migrating on silver-micas
with considerable DC voltage across them.