I assume there were no equivalent marks for the methane tank. If so, I'm guessing the downcomer is somehow serving the function of the internal baffles in the LOX tank. Either preventing voids or softening the hydraulic hammer effect. Then again, there may not be enough LCH4 in the tank to produce a large enough hammer effect to cause problems. There's almost four times more LOX onboard by mass.First the additional stringers on the S26, now new weld marks on B10: