Thanks for the info Ari.
We've (my old dad - ex-mechanic and I), spent 2 and half days on it now, but still no luck.
He pulled the DC motor apart again and found that a small part of one brush had broken off, and both appeared to be well worn. We sourced some other brushes from the variety of old car "bits and pieces" strewn around the garage, he filed them down and soldered them in.
Testing the motor it was very hit & miss on getting it to turn when powered, and when it did it sounded very rattly. He thinks the ball-bearing bush at the bottom is too worn.
So now I'm chasing a replacement.
Here's the other bit that was very strange... the oil pump.
Once cleaned and put back together, but without the first 2 bolts in it - the shaft turned nice and smoothly. Put the 2 bolts in, and slowly tighten... just past finger-tight, the shaft couldn't turn. Too much pressure on the 2 x fig-8 sections that the gears sit between locks it up. Looks like the rubber gasket is no longer thick enough to tighten the pump up, so we made a couple of paper gaskets to fit between the sections, just outside of the rubber gasket, to take the pressure of the centre section. Once we did that, I could tighten the pump up properly and the shaft still spins. ???
That problem may have led to the damage to the DC motor, stopping it from turning.... who knows...
bike is back together without an EHCS actuator attached, so at least I'm still riding..
If i can't find a motor I'll have to look at ordering the entire actuator (ouch).
thanks for you assistance!