No chance. If any fuel is leaked out of the vent system, it would be such a small quantity as to be irrelevant. Maybe it is the parafin 'dust' from the exhaust? I don't know exactly what it was, but when I used to leave my car under the approach path at Heathrow, after a few days it would be coated in a fine dust. Maybe that is enough to make the track a little more critical?