Just changed the small coolant pipe that goes above oil filter,has mine was leaking.While looking under the car i could smell slight petrol smell around the rear.
On seaching around i found the problem to be a rusty fuel line were it goes under the floor pan to under the rear seat.Two of the 3 lines were very rusty and one leaked slightly.
Car off the road now, i got some lines from a older impreza but the are notquite the same.
I would check your lines, mine is a uk 99 car and i was shocked.

 

I'd also check the pipe from the bulkhead to the engine, those go pop too