[edit: just a bit too late on this
Looking at the video, I would bet that either there is a pin hole or crack in the out dip tube, or the o-ring around the out dip tube is missing or damaged.
Before pulling the out dip tube for inspection, one thing you could try is to fill the keg with water, seal it back up, turn on the gas, and see if that sputtering stops. If it does, there's definitely a hole in the dip tube somewhere below the filled water line. If it still sputters, there may still be a hole, but it would have to be within an inch or so of the flange, which might help you to find it.
Still, all in all most likely it's the o-ring just below the out tube flange...