Just reading this and I think you are already looking in the right areas. The hole in the seal that Gary has pointed out to you is by far the most common cause of leaks as it allows water to flow down inside the seal into the footwell. I think if your windscreen was leaking it would be as a result of a poorly installed replacement screen so if you can see evidence it is not oem them that could be a possibility. Other than that it is just a case of trial and error until you locate the source.