roof leak cause?

[yawnbros]

I have a slowly worsening leak on the top room in my house. The house was built in 2003 with a study in roof space of the house. Several years ago a faint mark appeared on the inside slope of the roof(highlighted blue). A year or so later, marks appeared above the 2 windows and then more recently significant shadow marks appeared near the chimney (highlighted red). This has spread further and damp readings continue to show figures of between 15% and 23%.

I have called out some roofing guys and they have taken a look and applied some sealant in a few places but this has not helped at all. I have used a drone to take further pictures as attached but these don't really seem to show a clear cause. There does seem to be some faint cracks on the chimney and a few marks but I'm not convinced these would explain marks of this extent.

Any suggestions of what to do next or possible causes would be very gratefully appreciated.

[dewaltdisney]

I must admit my first thought was the lead flashing was allowing a steady drip in, or the chimney flaunching is cracked, but looking closely at the photos it is not obvious at all. The water stains would suggest a lead flashing crack in the fold where it tucks under the tile and as water always finds the easiest way down a crack will let in a lot of moisture over time. It is difficult to tell from your photos alone and it really needs hands on, close inspection by a proper roofer who does lead work. Sorry, this is not much help.

DWD