Changed for a modern flex, but the original earth was soldered directly to the all metal chassis. I have soldered a tag to the earth, and attached it to the chassis with a nut, washer and bolt. Metal all cleaned and shiny. Hope that is OK?
Curiously, although the mains lead was rubber, all the internal wiring is PVC, and looks fine. Probably constructed about the time rubber flex was being replaced by PVC?