Unfortunately the leak is at the top.  Initially I had thought the slots might be clogged too.  Even though the leak is coming from the top, I checked them anyway, and they are clean.  The water is running from top of the movable pane, down the inside, and pooling at the bottom.  Because of the window valance, I can't see the very top of the window.  I am going to have to take this apart to get a good look at it.  Luckily it is going to be warm and dry for several days, so I be able to look at it.

Has anyone taken the valance apart?  I may call the factory to see if they have any ideas.