Fuel filter can corrode under mounting bracket.
But then i guess you would have fuel spraying out when under pressure so probably not that.
+1 on this, if you haven't already checked the body of the filter you could have a really small pinhole leak under the bracket and the filter will take a while to drop to ambient pressure from running pressure after the pump is shut down. Worth a look and it takes a tiny amount of petrol to stink out a garage.
