So here's the diagnosis:
The motor is vibrating so badly that the connection plug (inside the machine body, next to the motor) drops off. If you bodge it back for testing purposes the machine has a dreadful loud noise.
Taking the motor out and investigating, it's the bottom motor bearing, inside the impossibly hard to open motor housing, which is making the noise and vibrating badly.
OH is not a motor expert, but says he thinks this is probably terminal for this motor, and replacements are not really an option for an old cheap ebay purchase
(Even if I knew how to find one)
If anyone has a miracle cure, please speak now . . .