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Minor leak at chimney #2

I have a minor leak coming from the corner where my chimney enters the roof space in the lounge (as shown in picture). Only a couple teaspoons coming through total overnight with heavy rain but something I would like sorted. I have previously had a tradey come around to address the same issue (both at chimney connection and skylight above kitchen) and he had applied some sealant from a cartridge around the chimney on the roof, but given the same issue has occurred again I'm wondering if a more effective fix is required, i.e. replacing the membrane on the roof surround chimney (and maybe skylight). House is double storied but on sloping section so roof can be accessed via ladder easily from ground level.