Swapping the motors is easy
Pop the glass off, then the round backing plate, push a flat screwdriver into the square holes with arrows on them to release it off the moving arms
Then you need a T10 torq bit and there's 4 screws holding the motor on,
then remove the rubber cover, there's another 4 T10s under it (2 in the middle 2 by the arms)
Then lever the 2 1/2s of the case apart pulling the tabs out the way.
Now you should have the actuator unit apart and see the moving internals.
Pull out the red circuit board carefully (there 4 pins on the back) rest it over, then prise the black plastic bit off the motors, again there's 4 pins in the middle and 2 pins on each end that go into the motors so don't bend it.
Swap the motors then refit.
Should take you about 1/2hr.
This is who make our actuators
http://www.magna.com/about-magna
I've emailed them to see if I can buy a motor.
I've found plenty on the net that are the same size but none have the 2 pin power input like ours so might not work.
I will let you know how I get on.