I suspect that your fuel leak could possibly have weakened the plywood on the formers that are glued to the bottom skin. But the glue (I think they used epoxy with a white filler) should not really be affected by fuel. Can you tell if a bit of former is still attached where the bond failed? Or does it look like the epoxy just came off of the bottom sheet?

From the other examples of this that I have read here, it seems like many of the past failures were simply a case of not enough glue used or not an adequate bond from the manufacturer.