The drive wheel had worn teeth

The replacement part arrived so swiftly I didn't know what it was until I opened the packet.

The motor drive shaft has two flanges on it that can accept a narrow wrench and the drive wheel can be screwed off clockwise!
Alternatively the drive wheel can be easily prised off and the drive wheel screwed on anti-clockwise thread.
Success
Of course if the drive wheel was made of a more durable material this would not have been a problem unfortunately typically american not made to last!