Subaru Repair: 1998 legacy-outback, legacy outback, subaru dealership

Question
I have this Subaru 1998 legacy-outback. I like it very much but the problem I am having is every couple of weeks or so there is a very strong smell of gas inside the car if you open up the back seat you will find a thin layer of gas under the seat. we have had a mechanic check it no leaks in the tank. no gas in lines under seat I call Subaru dealership and they said sounds like filler hose but mechanic checked found nothing physically wrong don't know what it might be or what needs fixing any ideas will help
Thankyou
Steve

Answer
The filler neck is the most common problem, but that shouldn't put any fuel inside the car. In fact nothing should put fuel in the car. It could be a line, or the tank itself. There are so many possibilities. I would recommend taking the car to someone that can SMOKE test the fuel system. This is a test where they can add smoke to the system and it should come out where the leak is. Good luck