[KyleTownsend]

I have a T337G model, and we recently noticed that fuel would still drain from the front engine fuel sump with the front engine fuel valve closed. Of course, we immediately suspected the valve. However, tapping on the check-valve for the fuel return line from the front engine back to the tank quickly revealed that this was the actual culprit. Might be something you want to check.

Of course, the fuel valve setup is somewhat different on the B models vs. my T337G, so these comments might not apply to your situation.