I have a 1988 325 ci which I use as a winter beater so I don't have to drive my garage queen 92 400E in nasty weather. The gas tanks are 2 piece units that all seem to fail at the seem over time. It's very common and I would bet it is why you smell gas. It's kind of a big job to replace the tank as the drivetrain needs to be lowered to do it. I only fill it up half way and it doesn't leak or smell.