Thanks shortbus, I have looked into a replacement motor but they all seem to be in America. When looking at the cost of the motor you then have to add shipping cost. That means a £60-70 expense. I find that expense hard to justify when the car is not a daily driver. Surly there must be an inexpensive way to hook up a 6vdc fan motor to 12vdc. I believe the motor is field would and when running it on 12vdc it draws 0.24 amps with fan attached. I have a 12V to 6V DC-DC 3 amp Converter Step Down Module Power Supply Volt Regulator running my fuel gauge. Could I not use this?Have you looked at a 12V replacement motor? Many of the old style fan motors were atached to a bracket with the same screws that held the motor together and since most car makers didn't make their own motors for things like this the motors were pretty much universal between brands of cars. So if this was mine I would just look at some of the places that sell old car replacement parts.
A lot of times the cars from that era used of brand heaters/defrosters too, since a heater was a dealer add on not something that came from the factory. Names like SouthWind come to my mind, but there were many more.