Advise/Help please :) - Leak or Condensation?

[LeightonL]

Hi I live in a 1930 semi-detached house with its original roof, its a welsh slate roof and since Storm Imogen hit us I have a strange leak/condensation build up in my loft In one area.

I've had a good look inside and cannot see any day light and outside there is no slipped or cracked slates, also a roofer has been in the loft and up to the area of the roof the problem is and cannot see any problems with the slates as they look fine.

I have asked a few more roofers to come take a look but this is being abit of a puzzle.

Here are some photos I've taken inside my loft of the problem.

 

[LeightonL]

Some more pictures.

 

[datarebal]

the slates are showing signs of water absorption/penetration. the rafter that appears very wet looks more like a leak than anything else.
should be easy to track. visual inspection might not show anything rip a few out.
also it doesn't not look a new problem