Well gang the rear window puzzle is at least partially solved. Today I picked up my trailer from Shorewood RV, where I had taken it for a replacement of the rear window -- the mother ship's Rx for the problem at hand.
Shoreview reported that the problem was due to excessive application of expanding foam insulation/sealant at the factory. The force of expansion during the curing process was enough to warp the endcap panels on one side, forcing the window out of plane. They had to remove the rear window and partially remove the rear endcap panels to scrape away the excess insulation before sealing and riveting everything back together. They said the tech billed 12 hours out on this job. I met the tech and it was clear from his demeanor that this had not been his favorite job of the week.
While not perfect the rear window does operate reasonably smoothly now, at least to the point where the window latches can be engaged without a great deal of fuss.
Shorewood RV does deserve some credit for their tenacity in dealing with the mother ship on this, and for being able to perform such a difficult repair.