My bedroom window is leaking seriously when there is wind rain, and when i check for the cause. what i can only figure out is that there is a little gap between upper side of the wooden frame and the concrete, while the window is flashed with the outer wall of the building. so when the rain hit the upper wall of the window it can easily penetrate the gap between the frame and get leak into the room, please how do i seal the gap to correct the leakage.