Andy, thank you for this great work in progress!!
After a long absence, I was nearing completion of my Bandai 1/12 Stormtrooper but was also experiencing a few fractures. I would have never thought it was due to mineral spirits until I read this thread. It just didn't seem like a wash could weaken the plastic given that I had primer, layers of tamiya acrylic, and a Future gloss coat protecting the plastic from the wash.
As a test, I dipped a piece of Bandai sprue into some mineral spirits (Varsol from a local Walmart) for 2 hours. When I took out the sprue and scraped it against the side of the bowl holding the mineral spirits, a layer of the plastic scraped off to my horror.
Andy, how are you going to avoid using mineral spirits for future kits? I would like to use acrylic washes but with acrylic paint and an acrylic gloss coat, I don't want the wash to affect the layers of paint below.