The problem might be easily solved : The lead flashing at the chimney extends underneath the roof tiles, The end of the flashing should be turned back on itself for about 3/4" , the reason being that if wind blows rainwater up along the flashing it cannot go any further than the bend.
With the recent storm (heavy rain, strong wind) conditions were perfect for rain to get under the rooftiles if this bend was not in place. If you are handy with a ladder & not afraid of heights it will only take 10 mins to rectify & cost you nothing.