Ok, I was a bit worried you might be about to rip out the dash in an attempt to fix your leak.
Good that you've proven the sunroof to be innocent in this. You now know it's the windscreen. IMO the only way to seal it properly is to remove and refit with butyl screen seal which can be found on eBay, and various other posts I've made about windscreens. It's not a difficult job, you just need to take it steady and not stress the screen taking it out. Another pair of hands is essential for moving the screen.
Good that you've proven the sunroof to be innocent in this. You now know it's the windscreen. IMO the only way to seal it properly is to remove and refit with butyl screen seal which can be found on eBay, and various other posts I've made about windscreens. It's not a difficult job, you just need to take it steady and not stress the screen taking it out. Another pair of hands is essential for moving the screen.