I have finally got my series one sport tailgate motor and mechanism working well. Firstly, the screwjack mechanism needs to be re-assembled fairly carefully. The casing screws of the worm drive and the end shaft nut need to be tightened carefully and not too tight. To loose and the worm drive jams, too tight and it binds. That is why there are anti vibration washers on all those.
Now to the motor. I believe the series 1 is different to the series 2. On the series 1 they use a Ducellier motor quite often used as early Ferrari and Maserati window motors. They can be very powerful and high torque motors. I say can be because they can be wired up two different ways depending on how powerful you want the motor. The motor has dual opposite wound field windings, so reversing the motor dimply uses the other field winding. That is why there are 2 positive wires coming from the switch. There is a third positive wire coming from the switch that goes direct to the brushes and a negative earth wire from the motor. Using all 3 + wires makes the motor too powerful for the job and the micro switches will be rammed hard.
The not so powerful method is to use the two field winding positives and use the wire from the motor that would have connected to the third + from the switch as the earth on the frame of the screw-jack. That leaves one unused wire from the switch and one from the motor (the original earth wire).
I have found an electrical workshop in South London who are experts in fixing/re-building these motors so if you are having problems with yours PM me. As you probably have found out replacement motors are as common as hens teeth.
It is also essential that the limit switches are adjusted correctly otherwise the whole mechanism could overrun and either jam or overload the motor.
Hope the above makes sense