Re: 2008 STi - Broken welds on rear roof support (metal on metal squeak)...
I stopped by the dealer on lunch and spoke to the service manager. I showed him the video from Saturday's test drive and what we thought could be the root cause. There was expected speculation, but he seemed receptive and said that he would order replacement dampers for the hatch. His reservation was this; without the dampers holding the weight of the hatch, there is more pressure on the potential problem area, thus stopping the squeak.
Anyways, he also has sun visor clips on order, because in the midst of all of this work mine were broken. I will continue to drive the car without any plastics on the hatch and the dampers removed. I'll update the service manager when I pick up the visor clips later in the week.