Thanks! It was much easier than I thought - didn't have to remove the aft sash - just removed the top phillips screw and the two 10mm bolts holding the sash to the door panel. That allowed the sash to move just enough to slide the replacement glass/rubber gasket into place. 30 minutes!
However, upon initially removing the gasket, we found the culprit to be poor assembly at the factory. Half of the bottom rubber gasket that is affixed to the door [non-removeable] had been folded over when the glass was originally installed thereby creating a "torque" on the glass piece which likely caused the spontaneous shattering on a day where the temps warmed after a cold night.
I plan to alert Subaru USA to this issue with the hope that in the future their quality control/training can be a bit more stringent.
