Re: water leak at top of window casing
One other thing for you to check. You said you have a window directly above this one and it only happens during wind driven rain. I don't know what type of windows you have, but if they are double hung windows, I have seen wind blow rain under the sash and over the back of the sill. It then drops down on the window below. If this is the problem it can usually be solved by caulking the crack where the sill runs under the stool.
Be sure you live your life, because you are a long time dead.-Scottish Proverb