Todd,

Water is powerful stuff.  I am not sure how your weather has been this winter but if it has been any thing like what I imagine it has been back and forth below and above freezing several times.  The water in the tank could have cycled several times from liquid to solid.  I can imagine the water getting behind an edge of the pro seal in the corner of the tank and freezing lifting the seal from the aluminum.  If this happens several times I could see the water working its way completely under the pro seal.  As for the time lag between when you put the fuel in the tank and when it first began to run out I can only suppose that the temps in that part of the world are steal hovering around the 0 c mark at night and only getting above 0 c during the day for a short period of time.  It could have been that there was ice in the area between the aluminum and the pro seal, and it took that long for the fuel to thaw through the ice.  Of course this all supposition, a product of an over imaginative what if mind.