[Chas]

Hamilton, you normally don't replace the mica caps. The 2 in part 50 are mica and don't have to be replaced unless subsequent problems point to a failure.

I will second that restoration issue. Overall genuine mica condensers are "most" often found in tuning circuits. "Shotgunning" them is a real recipe for radio disaster...

Even, twisting them on their leads to read the "dots" risks fracturing the bonds to the metal foils internally as the copper wire extrudes during the twist moment.

The "best?" time to determine if there is a mica condenser problem other than split open, blistered, burned or broken lead wire is to; Complete the restoration and operate the radio. Poor sensitivity, dramatic calibration errors that cannot be "aligned out".
If the "desire" is so strong to discover, gently de-solder one lead wire and take a measurement.

One company MICAMOLD made both mica capacitors and paper caps under that name. As a "general" rule rectangular Micamolds are paper, starting value of .0001mf.

The square Micamold is mica values from less than .0001 down to FWIR 10pf. are mica and may also have temperature compensation, the dots tell the story

GL

Chas