Leaked but not all the time

Hi all,

4 years ago, we built an exesention on our garden as we live in a one-bedroom flat, but with an unexpected child appearing we need 2 bedrooms. so built out into the garden.

Issue is we have some sort of a leak. well, a wet patch, in 4 different places.

It can rain all day and be fine. nothing. but if we get a wind and it in certain direction. (Not works which direction yet) it starts to show wet patch.

I had the flashing done twice by the people that built it. they said they done it right.

The roof is fibre glass. I also had another roofer said the hight of the fibre glass going behind the lead flashing is correct. It was a thought that the wind might be pushing the water up and over. I was thinking if I could do something to sealed the lead to the roof. Then thinking the roofers would of thought off thought of that.

I cannot understand why it happening, they said the crack in the render higher up (Flat above me could be causing it and letting water in.). Now I have these filled in by renderer and he also rendered a slope above the flashing saying this will solve the issues (See Pics.).

This has stopped it in 2 x places where it was bad. But it appears in one place still and another. the strange thing is. both wont leaked at the same time even thou they on the same side wall and only a half a meter apart.

I’m running out of options and no one can give me a straight answer, I not manage to decorate that room since because of this.

So I’m here to see what options I have. I wonder to pay someone to ripped this all out , and redo, or should I sealed the leading at the bottom see if this solve the issue?

Really don’t want to chuck money at it. the new building is not built into this house. Just like joined together.

Need more info then let me know