A couple of years ago we owned a P reg Galaxy and had exactly the same problem. We tried everything, even got the windscreen re-sealed. One of the old mechanics in our village could not find out what was happening, then I registered with a site just like this and the answer was found. If you lift the bonnet there is a gully where the rain water runs off the windscreen and in both ends of this gully is a hole which drains the water through a pipe down into the wheel arch to run away. This hole in the wheel arch gets blocked from muck off the road and using a metal coathanger that has been straightened, my husband cleared these holes. This cured the problem. I have now purchased another Galaxy this weekend and one of the first things we are going to do is clear these drain holes.