++safety Alert++

[FMild]

Jim,
I'm by no means an expert but I've learned alot about my "D" model (non-turbo'ed) in the last two years with malfunctions due to the a/c sitting awhile. The most relevant one to your situation was after doing some work with the fuel selectors moved to "Off" I couldn't get the front engine to start. I'd prime it & it would pull away from the starter but then die. Turns out the fuel selector didn't make it all the way from "Off" to "Left." The little ball/spring deal which gives the feedback of the detent was gummed up and I truly wasn't getting it into the detent. They need to be lubed well & watch for track wear on the plate if they're not which will cause more problems.
That being said if you didn't move it at all then the only apparent culprit is the valve itself. I understand from the manual that you have an extra return line to the sump but that wouldn't cause it all to burn from one tank. I would suspect you have an internal failure in the valve itself which allowed the valve to port fuel to the front engine. I'm interested to see what you find.