One other item to check is the small vent hose and connections for the gas tank venting system. These are located on either side of the fuel filler neck on the gas tank and connect to the funnel shaped vent thing on the early cars, and to the vapor return tank on the later cars, which is what you most likely have on your late model 113. It would appear from the thread of conversation that the fuel line is the most likely candidate, but this is one more thing you can look at.
Note, these two vent connections are under the protective cover for the fuel filler neck you see from the inside of the trunk, held in place by sheet metal screws.
