As you may know, InterNACHI has partnered with Home Depot and publishes their articles. Here is the latest: http://www.nachi.org/home-depot-replacement-windows-energy-efficiency.htm
I am happy Home Depot is sponsoring us.
Moisture in the wall assembly around windows is a concern.
Metal glider/slider doors and windows circa 1970’s can be an issue.
Please, look at the drapers in the photo of the gliding/sliding doors on the second-floor cantilever bump out.
Two concerns. 1: The soffting below. 2: Full-length drapes to the floor.
I suspect due point condensation.
I also state that $1000 per-pane is highly suspect. I would recommend an IR and inspect the interior assembly. Even a pressure water test on the envelope.