I know there is an o ring in the demand valve. Im thinking its around that valve or around the fill hose. I think the crud is built up from repeated fuel seeping. Was just hoping someone was familiar with this issue. I sprayed soap around the connections, sender etc and dont see any obvious leak. Tank is holding pressure, when I open the fill cap I can hear a rush of air. Maybe BCB can guide me here. I know there were some tank issues around the time. Ill let them see the pictures and advise before I start cleanup.