Since its not penetrating the decking of the roof, this is even more difficult.
I would find the drip of the leak, then begin a on the knees inspection straight up the roof from this exiting leak. You might find that it leads to a stack of some sort, or a nail that has popped out and letting water in, or a shoddy roffing job where a throat of a shingle is exposing the previous course of shingles. I cannot imagine that this leak is very far up as it seems impossible for it to go around so many obstacles.
I would first look at these areas: valleys or flashing, stacks, popped nails, and visible holes.