take a look on here for a Nissan Bulletin that explains how to service the 5th bow motor which is the first thing that moves on the roof after the stow away clam opens. There is a procedure that tells you how much slack should be on the worm cable, how to re-feed it through the motor using an external battery and is really easy to follow. At least the dealer should have known about this and should have looked as it takes 15 mins to do and can rectify your problem, If I can find it, ill post it up.