[Mondial]

Looking at the schematic, the cap in question C46 appears to be a common value .01 uF. It is important that it be replaced with a high voltage film cap of at least 1600 V rating, as it is directly across the full high voltage secondary winding and is subject to the additional switching transient spikes. Check and see what ratings are printed on the original cap.

I would hold off on replacing the small metal can cap located between the transformer and filter choke, at least until you get the radio working. This appears to be the RFI suppression cap 45 and/or 47. It is specially constructed to act as a low impedance bypass to ground for the hash noise created by the switching of the vibrator contacts. This sealed oil filled cap should be pretty reliable with only 6 volts across it and it may be difficult to find a suitable replacement.

As far as a solvent for final cleaning of the contacts, CRC contact cleaner should be fine as long as it is the type that does not contain any oily residue or silicone protectant. I have also used 91% isopropyl alcohol with good results.