House is 15 years old and in the last few weeks noticed these wet patches occurring when it rains. (Upvc) Window is dormer on the the third floor, with no brick work around it- only flashing and tiles. Wet patches are only occurring on one side of the window. looked at the drainage holes on the inside of the window but there doesn’t appear to be any wetness around them so I guess that’s not where the leak is coming from? Any ideas? Thanks!