[Arran]

Even if you are not restuffing the paper caps, which is surprisingly easy to do I found, don't toss them out, save them for a future project or put them in a bag and keep them with the radio. I think that Kirk may be right about that chunk of cardboard being the remnant of an old box electrolytic cap, since there are no cans or mounts for cans on the chassis then they would have had to use something like that. The dogbone resistors are not especially trustworthy, code is read this way, Body End Dot, 1/4 Watt carbon comps of any type should be checked, and if more then 20% off changed for 1/2 Watt ones.
Regards
Arran