Fuel filler neck question

I have a 1995 Ford Taurus, 117000 mi. I suspected a gas leak recently because I occasionally smelled it and my gas mileage was deterioating. My ford dealer mechanic told me the filler neck was rotted and that was what was causing the problem. I looked underneath the car at the pipe and didn't see any leakage or rotted metal, just rust. Do you think he is referring to a part of it that's not visual (like the part where you put the nozzel of the gas pump)? I already spent money on a salvage part to replace the pipe 'cause ford doesn't make it anymore. I don't want to pay extra for the labor if the part doesn't really need to be replaced!