At this point I merrily spent half a day putting the hood back in the car to find it didn't work. The motor ran but no movement of the hood. I have been raising and lowering my hood by hand for some time and the pressure bypass valve in the pump body behind the Bowden Cable assembly had seized open.
Off with the hood again, rempove the black plastic cable / lever assembly, use a 5mm socket to turn the brass plunger and work it free. The plunger should spring out, mine was siezed in. A drop of light oil to lubricate the seal and check the action and back together.