If I remember correctly, an exhaust leak will cause it to run um... rich? So, maybe you're smelling unburnt fuel in the ehxaust... until the exhaust heated up enough to get a decent seal around a gasket?

But yeah, if I smell fuel on a 3800, I immediately check to see if it's pooling up around the injectors. That's going to be the source of the engine fire. The o-rings eventually go bad, and the rail is aluminum - and bends fairly easily - say, when installing headers... or spark plugs...