The leak is on the forward facing side of the tank, 3/4 up. It's a 1" long indentation (i.e. no hole) that had an epoxy putty patch on it. My best guess it that the patch was there for at least 4-5 years, including all the time the truck just sat outside.
I JB Welded it last night. We'll see how it looks tonight.
Jim: Somewhere along the way as I was contemplating the truck someone told me parts were plentiful! I kind of assumed that while obscure, something like a plastic gas tank would be relatively easy to find. Alas, no....