I would mirror Martin's/James' comments in so far as there always a slight 'machine oil' smell. Not really the smell of petrol though.
Thinking about it though - if it was an actual petrol leak, I would imagine it would smell a lot stronger of petrol. Think about opening a jerry can of fuel for a few seconds - you can clearly smell petrol from a couple of meters away.
You could always steep the bilges in some industrial degreaser for a week or so to make it smell all lemony, then rinse and see if the petrol smell comes back? Even if you have no leak - your bilges will smell lovely!



