[Arran]

Rogers built sets used to use a lot of rubber (or gutta percha) insulated wire as well, going back to the early 1930s, they did not use it on the leads of the power transformers at all, nor much on the coils or IF transformers. My observation though, from working on a Rogers Ten-60, was that the white and yellow coloured stuff held up the best, the green and blue held up the worst, and the red and black was somewhere inbetween. Rogers had a connection to Grigsby Grunow in Chicago, who was also infamous for using rotting rubber wire.
Canadian G.E and RCA sets also used a certain amount of rubber wire, but they also used the cloth covered, I'm not sure why they mixed the two. It's weird stuff, some gets hard and crumbly, and turns to dust when you look at it the wrong way, but in other cases it gets gummy and dissolves off the wire.
Regards
Arran