Ok, all done and can't believe how simple this was in the end

Nothing electrical about this problem except that the sunroof was meeting some extra resistance when closing which was activating the safety reverse mechanism. This was down to the small wind deflector at the front of the opening, which is supposed to close down as the glass approaches it thanks to the roof bearing down on two arms either side of the opening.
In my case the wind deflector was not closing down quickly enough to avoid fouling the front of the roof and activating the safety. Solution? adjust the mounting points for the two arms (underneath the screw head the hole is elongated to allow adjustment), and reset the arms as far back as they will go. Now when the roof closes the new adjustment means that the deflector deploys to a shallower angle which doesn't catch the roof. Simples!

Thanks to those chaps who offered advice and those who offered nice cheap replacement motors, but for now I'm very happy!
