Between the tubular extension housing and the mount plate for the fuel pump there is a O-ring that goes between the two parts to provide a leak proof seal for the racer. From time to time the O-ring dries out and cracks or if you tear something apart the O-ring swells from fuel and will not go back in it's home.
RBS carries a full supply of O-rings for this application. O-ring measure 1.5 x 41mm and are sold each.