[Arran]

 I found that when you have a dirty looking capacitor the best thing to do, before melting out the contents, is to wipe the dirt off with a paper towel soaked in mineral spirits, that way the dirt can't work it's way into the cardboard. But if it does you can remove it with some lacquer thinner, which is also useful for removing residue from that hard, dark brown wax, they use to plug the ends.
It sounds like another lightning strike victim, I'm working on one right now, but unfortunately the donkey who worked on it last pulled out the original antenna coil and wired in an external ferrite bar antenna, so I need to see if the substitute I found will work. But before I can do that I have to finish overhauling the rest of the chassis, I've never seen so many open resistors in all my life, not drifted but completely open. Like your 42-720, this radio must have had a lot of hours on it, not quite run into the ground but still.
Regards
Arran