I have a turbine type ventilator installed on the roof. It was installed
several years ago to improve a humidity problem which has since been
resolved.

Within the past year we have noticed a slight leak in the kitchen pantry
exactly beneath the ventilator. Water is evident only a few time a year and
I cannot determine where it is coming from. I inspected the ventilator but
did not see any obvious cracks in the base. I applied tar around the base
in case there was a crack in the roof near the base, but the problem has not
been solved.

The problem appears only certain times like after a heavy rainfall or snow,
but it is not always consistent.
Any ideas?