A surface went transparent on me, so I figured out the change transparency command for a face, but it only works sporadically. The surface in question has never gone solid again, but adjacent surfaces can be toggled a few times between visible and solid, and then they give up and go transparent.
The first toggle of a surface from solid to transparent works. Then SHIFT-select to bring it back leaves it transparent. Sometimes, they can then be made solid again. Now I have a whole mess of surfaces permanently transparent.
***fixed it!!! Individually removed all appearances from all faces, bodies, etc, using SHIFT-select when necessary***
Only posting so I can find this later. Easiest place to find solutions I figured out.