Ok, the motor is in the boot under the luggage cover. I lifted up the cover and low and behold the motor and foam padding that the motor sits in was about four inches deep in water. Drained all the water off and ordered new foam padding from BMW (£25). The motor unit must have been really really cold sitting in that water in these minus temperatures. Dried everything out thoroughly, then drained off the hydraulic motor fluid and replenished with simple Hydraulic jack oil. Operated the roof up and down a few times and all is well....Drilled a tiny whole under boot floor at its lowest point to help prevent this happening again. Think I got away with it....PHEW
