Thank you for your reply. Unfortunately I live in the south west so too far to bring it but I appreciate your advice ( unless you’re coming to Cornwall with your tools) for info the roof motor is in the boot.
I have the same issue on my Z4. I took it to an approved BMW specialist and they advised that it isn’t the motor as it would struggle to come up not down. They suggested topping up the reservoir for the motor and lubricating the wires for the roof mechanism. I haven’t had time to try yet.