Leaking front windows is an age old problem. Some do and some don't. Leakage can be from around the seal between the window and van body and can also be through the outer frame and rubber seal. In my previous van I totally removed the window and reinstalled it following instructions given to me by a local caravan repairer. Leakage still occurred. It wasn't until I used the pressure washer on the window that I found that water entered in through the two drain holes in the lower edge of the frame. If you run for finger around the lower edge of the outer frame that holds the glass you will feel two slightly raised sections and that is where the water entered under pressure in my case. As to the fix,it would appear that a new rubber should be fitted and steps taken to ensure that the window be firmly secured. I did not ever effect a repair but did make sure that my new van did not have a front window. Cheers