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I've followed this thread out of interest and I have some questions/observations for the OP. I don't understand how the pigeon droppings could cause a leak as you describe as there is (or should be) a waterproof membrane under the tiles. If water gets under the tiles, it should flow down the membrane and not penetrate the interior unless there is a break/hole in the membrane itself. The only place where water might get under the membrane (barring a hole in the membrane itself) is around the flashing where the vertical wall meets the roof . So I guess I'm asking, does your roof have a membrane under the tiles, and just where in the photo do you suspect the blockage has occurred?

IMO, a more likely scenario is the wiring is conducting the water into your garage from some remote location, not associated with the area above the outlet. Not knowing where that wiring runs can make tracking down a leak difficult. Do you know where the wiring in the outlet leads or the path it follows? Some of that wiring looks like low voltage/bell wire or telephone wire. Is there any place where the grey wire exits the interior of the garage? The leak may even be from a window, if the wiring passes through the framing under it.