Roof leak

A stain appeared on the lounge ceiling, east side 1m from the doors. This is in a tricky spot that is difficult to get to from  either the inside or the outside. There is a gully that had 2 clumps of leaves, and the wet ceiling is between the 2 clumps. We had just had 45mm of rain. From the south guttering the leak is 3rd row up, under the gully.