SOLVED IT!
So I've had a merry evening this evening re-cleaning and re-oiling. The capacitor in the pedal went yesterday so for good measure I rebuilt the carbon stack, chucked the capacitor and swapped out the 13A for a 3A fuse (safety first!). And then a re-adjusted the belt tension and the motor alignment.
Wow, it's like a different machine! I'm a very happy bunny!