Clare,
I guess I missed the part about the oily motor. I don't know what chemicals you have available to you in the UK, but I have used denatured alcohol and aerosol break cleaner to degrease really gummy motors. Break cleaner is designed to remove all traces of oil on break parts and it works good on other things too.
Keep it away from the machine and use it outdoors, but it will clean the motor.
Joe