Persistent dormer leak

[Bid!]

We live in a house with a dormer extension and for the past two years we have had constant leaks from the roof/ceiling that covers our back bedroom. We’ve had 6 different roofing firms out who have changed slates, refelted, re-leaded, patched up the flashing under the dormer window and it’s still leaking. We know there is a beam that runs across above where the leak is appearing and we are wondering if that is causing it? Insurance won’t cover, any advice or similar stories? I’ve attached photos of the dormer window and the ceiling

 

[blup]

Are you sure its not a leaking pipe from ch supply pipes or loft water tank.

 

[Bid!]

Thank you we’ve checked, no pipes and only leaks when it rains

 

[DAZB]

My suspicion is it could be the window itself and if water is getting into the channels of the frame due to old seals etc...it could be travelling through the frame via a crack, overtightened screw, bad sealant etc and gaining entry that way.

 

[datarebal]

Firstly there doesn't appear to be enough lap from the flashing to cover the slates.
Doubtful there is a correctly formed tray under the window