[morzh]

http://www.antiqueradios.com/philcorestorer/page6.html

This discusses mica caps. The bottom line - usually no replacement is needed, unless there's a physical damage.

Mica caps of old type were "clamped type", where copper foil was clamped together with mica sheets. They were very unstable in tolerances, as there were airgaps, and the clamping mechanism provided the pressing of mica sheets against copper sheets.

New caps are "silver mica" ones, very stable and non-degradable.

I am not sure whether pre-war Philcos used clamp type or not; post-war used Silver micas.

In any case, if no physical damage is present, and the value is where it should be, those caps could stay, unlike paper caps, that do degrade over time..