I talked to my distributor about a month or so ago Conner and he said it is likely that I didn't have the coating thick enough. He said it was designed to keep moisture out, not contain liquids, and that it is possible that a "balloon" is forming in a void then getting thin enough to allow a leak. Since every screw head, seam, and other void was filled with liquid nails and subsequently mesh tape and all fall on 2x6s, I don't believe that is the issue. Especially with all the extra coats.
BOR, if you remember early on my original plan was to have a liquid rubber coated frame around the window securing it from the inside. I'm thinking that may be a potential solution.
greengiant, NOLAGT, kallamond - Behind the drywall is a solid wall of wood around the window. There's no way to see anything with the drywall removed. Also, there's no way to get anything under the tank.