Just to get some closure on this thread, it was indeed the selector switch. It kind of disintegrated as I took each connector off and had obvously been fried (or grilled, probably). Fortunately the connectors were all in good shape, except their shrouds all broke up. So as I swapped each connector I wrapped it in heatshrink sleeving. I now have a fully working oven again. I couldn’t load photos to the forum to show you but they are here:
https://flic.kr/p/2m21Z3T
https://flic.kr/p/2m1RRq8
Thanks Dave and KWatt.