[Arran]

I would reccomend leaving the micas alone unless there is obviously a problem as they tend to be in RF circuits and you can cause more harm then good by replacing them. Deterioration isn't as much of a problem in a battery radio as there is negligable tube heat, but even so the paper caps do age and old carbon composition resistors do drift, on occasion these sets have electrolytic caps usually a single small one. So the ones to replace are paper capacitors/condensers, the electrolytic capapacitor (if it has one), any resistors that have burned or drifted more then 20%.
Regards
Arran