You're likely not leaking gas but you're venting out gas fumes from some where through a very minor leak in a line. Subaru did issue a recall for this but it was only on the Imprezas. I don't remember the specifics of the recall either. You can call any Subaru dealers service department and get an answer on what it was.

Personally I would check the ends of the rubber fuel lines going to the fuel filter first because that is a common culprit on any car....especially those with rubber lines like yours.