I've got a 1989 Coupe 2.2 E that's developed an annoying intermittent fault on the passenger window. Every now and then it won't go up. If I push the button down it works fine but just not when I try to raise the window. This happens on the driver's control button for the passenger window as well. Both times it has suddenly started working again for no reason (the next day). Does anybody have any idea what the problem could be???