I've just replaced some worn and broken friction hinges on one of my uPVC window units. When I removed the screws retaining the hinge to the bottom of the frame there followed a rather fine fountain of water from the screw hole! Simply by the height of the fountain Im guessing the frame was 1/4 full of water. I doubt I'll find the cause of the water entry and therefore cannot stop it getting in but I cannot see anything at the bottom of the frame to drain any water. Would it be ok to drill a small hole right at the bottom of the frame, just above the sill, the let the water drain?