Is this a known weak point, or just a process of elimination, given the evidence? (This is the point I had got to.)
I'll dismantle a bit tomorrow and see what I can find. I had dismissed this sort of problem as the stupid machine always seems to right itself between 20mins and an hour later. So had thought it must be temperature.
I guess that it could be some 2cent piece of spring in the switch stoping it rotating quite far enough to close the final contact. I'll be ready to scream if it is just a duff crimp on the wiring loom!
Any solution will be a huge step forward otherwise there will be an extra Scenic on the part exchange list!