Take a pic of the area from a little farther away. If I am seeing your pic right, That is the corner of the transom where the transom meets the side of the boat, and those bolts are the swim step bolts through the transom, right? If so, then is the spot with the old carpet glue is actually the fuel tank, and not the side of the boat?
Regardless, if that is fuel leaking out, then it must be coming from the tank, and yes the tank must be removed and replaced. No one in their right mind will attempt to repair a fiberglass fuel tank.