You did WELL to order a NEW tank. Once they start leaking, toss 'em. I've used a few lbs of grey epoxy in my day on leaky gas tanks, and it may do for a season or 2, but the rust always spreads and the leaks worsen. Does your new one come with 1, 2, 3 or 4 vents? That seems to be the only real difference in the pre-Formal tanks, as best as I can recall from shopping them/ Thus far, I've been blessed with a fairly NEW tank that came on Mathilda to help sell her. I got a HELL of a good deal, as it turned out.
I look forward to your report.