I think a little WD40 or some lubricant that can stand up to cold weather in all the joints will help. Any moving part that gets moisture trapped in there will be a problem, not just for MINIs. In the 80's I always kept all the joints in those pop-up headlights well lubricated and never had a problem with the headlights not going up or down when required. Also, use a bit of silicon lube on any rubber weather stripping will help the windows. I noted that once, when I opened my door this winter the window did not go down a bit to help equalize the air and when I closed the door after I got in the car, I almost broke my window against the door frame.