I opened the Tank today to inspect further, and discovered two of the standoffs the gearbox is attached to are broken. The gearbox is butted right up to the hull, so I resubmit my initial suspicion that the assembler cracked the hull while installing the gearbox, or when the upper and lower hulls were joined together. The other scuff marks you refer to have nothing to do with the crack. If the crack was caused by an external impact, the scuff marks would be closer to the crack.

It was actually longer then three days that I discovered the crack, so weather you find it "possible" or not doesn't matter. Because the lower hull is angled at an extreme angle is probably why I didn't notice it right away.