Leaking when it rains? Where in the hell is this water coming from?

Ok so after the above mentioned clean out of the cowls etc... Had a big rain and still leaking the exact same way. So I suspect even though the cowl drains were clogged, the leak must be coming from the corner of the windshield. So I assume I have to remove the windshield in order to fix? Any thoughts? Lets say I replace the windshield, when they remove the glass is it possible for me to seal the potential rust hole that might be in that corner? Is there anyway to visually see the rust hole from under the dash? I do have one of those small snake cameras