I recently purchased this fine piece of machinery for my Fiance. When I test drove it, the owner insisted on pumping the gas for my test drive as it was on empty. I thought this was a kind gesture but upon my first attempt at pumping I realized why. There is a leak somewhere! I thought at first it could be an overflow or something but I checked and it leaks as I pump and only then. I took off my driver-side rear wheel and found residue on the backside of my trunk (boot) right where the gas pipe comes out of the trunk. I tightened the clamp around rubber piping that is between the trunk and the tank. I got someone to pour gas in as I watched and there was no leak. I could here air escaping though (I was in my trunk looking through the access hole) I think the lack of pressure from the gas-can is why there was no leak at the time.
Can anyone help me?

Also if you have time, my check engine light is on. The car will sputter and die when in idle for an extended period of time. I believe the light and this problem are related. I am a beginner at the S90 it is nothing like my old 83 240. Thank you