Leaking Dormer window a roof leak or failed window?

[MacLaverty]

We have lived in the house for 1.5 years but we had high winds and driving rain last night and woke up to water coming out of one of our attic bedroom dormer UPVC windows and down the wall, but from within the frame itself which has never happened before. The pictures below shows where the water was leaking out of from both inside the bedroom and from outside. We had window fitters out today to pop the glass but without going onto the roof they were unable to get the glass out but managed to get the beading out and the UPVC drainage holes etc looked fine. They were adamant it is a roof leak but there is 0 other signs of any sort of leak up there, ceiling and walls are painted white so would show easily. For now I have put sealant over that corner and will keep an eye on it. Can a roof leak cause water to enter a UPVC window frame as I always thought the leak would not have chance to get into the frame itself and present itself around the frame? I hopefully have a roofer coming out to have a look but surely if there is enough water to get into the frame there would be clear signs of a leak elsewhere like the ceiling? Or am i more looking at a failing window?

 

[manimalism]

similar issue on my end once upon a time. with a partner on the inside and me with a garden hose on the exterior of the suspect window, i aimed water flow in controlled amounts around the perimeter of the suspect window, pausing at each corner to give the water a chance to work its way indoors. this i recommend to you. granted, this method is akin to setting aflame the contents of a rubbish bin to test smoke detectors, but for the brief time you're soaking the area, you should be fine. test the corner you sealed using this method.

vinyl window corners and seams are welded and these joints can, and sometimes do, separate with age with a nearly unperceivable gap. water is insidious and will find its way across an invisible split via capillary action. if found, silicone is your temporary solution until the window proper can be replaced at a more convenient time, as i do not believe vinyl window can be mended in situ. all this, of course, presumes a window structure failure.

don't rule out a perimeter sealant failure in some place along the intersection of the window and casing--again... test with water.

rainwater intrusion may originate higher up from the window (implying the window, as the fitters protested, not the culprit). the facia, roof proper, or the ridge vent might be the source. again... test with water.