if it is a noise suppressor and as such .22 would not do much in that regard
22mfd would be much more likely for that application
much more likely to be a filter capacitor for the field current to the brushes, i see a transformer, so it is my belief you have a transformer controlled generator. and they used larger capacitors to smooth the field current. 22 mfd would be what one would expect to find for that application.
check to see if one of the leads is connected to one of the brush holders, and if that is the case 22mfd is what it is.
.22mfd really has no application in power generation having anything to do with field current, and where this one is located there is no other reason to have a capacitor.
you can have it tested, but it is so old that it is likely to have drifted so far from spec that the results might be very misleading, that and the tolerance to start with was probably 20% either way, so even when it was new it might read 16-24mfd.
if there are two of these in this unit, replace them both, if one has failed the other is soon behind it. also when it comes to this sort of capacitor, you can go with a higher mfd rating, however do not go with less than the 600volt rating. more mfd' will provide more filtering, which is not a problem, less volt rating and you might have one explode on you, and you get to do it all over again, plus get to clean all the shrapnel and electrolyte residue out of the wiring, brushes and where ever else it gets blown or sucked into.
bob g