Yeah, the break was 100% from the trailer tongue getting slammed up and down from the bus overhang. Every bridge, every dip, every rise... With the slop in the ball mount, it was actually deforming the bottom of the ball mount. I shimmed it, to remove the slop, but I think that made it worse, as the damage was already done. The tank on the trailer tongue was empty (future extra tank for the bus), but I was likely pushing the 800# rating of the ball mount already. The new one is rated at 1500# with no slop. I used it for about 300 miles, and there isn't even a hint of wear from movement. Problem solved
Pucker factor: I saw the shower of sparks, started applying brakes, felt the trailer slam into the bus and saw it fall back, pulled over... Pretty robotic actually. I kick into survival mode when something traumatic happens, lol... Adrenalin kicked in after.