Three upstairs windows do the above when it rains. They are not next to each other and are in both the old and new part of my house.
I have been out and looked at the guttering, roof above etc. No sign of any issues anywhere. As you can see there are tide lines and it is destroying the plaster. None of the windows have condensation in them.
So what on earth could it be? I have read about drainage holes but cannot see anything on the windows that could be drainage.