Could also be a blocked pipe from where the wiper mechanism is. I noticed on mine that the black spongy stuff in the 2 air inlet at the bottom of the windscreen (Plastic cover plate for wipers) had brocken up. I took the whole thing off, removed them and replaced with some stainless steel mesh, and cleared the drainpipes. I never get moisture on the inside of my windscreen.
Just thought it was a good tip. As for the opipe for the windcreen wiper. just fill up the resevoir and if it does not go down within a week(as long as you dont use it), then the problem is else where.