[Arran]

If it's working on all three bands then the mica capacitors are more then likely fine. Actually if it seems to be working properly someone may have already overhauled the set and replaced the paper caps as well as the electrolytic filter ones, it may be worth checking to see if someone restuffed the bakelite block condensers. If the filter caps have a 450 VDC rating that is more then enough, if they look reasonably new, like a sealed aluminum can with a shrink wrap label, or have a date code that indicates they were installed in the last 20 years they will probably be fine as long as the set has been powered up on occasion since they were installed. You could replace them if it worries you but that's up to you.
I've never had an electrolytic short in an operating set, all of the ones that shorted out were from cold starting a long disused set without using a variac or a dim bulb tester to slowly power them up. Tha being said I wouldn't trust a 50+ year old filter cap, definately wouldn't trust a 70+ year old cap of any kind.
Regards
Arran