[Arran]

The RCA 100 loudspeakers also have a paper cap in series with the coil, so that may cause distortion if it is failing. The power supplies are fairly simple, electrically, but it would probably be a good idea to replace the paper filter caps for reliability, you can find substitutes at Mouser, along with some of the antique radio restoration suppliers. Antique Electronic Supply can furnish replacement audio interstage transformers that will work with the Radiola 17 and 18 type sets, unless you want to try a solid state substitute, The front ends of these are fairly simple, basically just RF coils with some neutralizing capacitors, not sure how reliable the resistors are but that's easy to check.
Regards
Arran