Looked like the first thing was to replace the ground glass. There's a nice Youtube Video, just had to order the stuff.
Followed the video. Had four pieces of glass cut. I ground for an hour each. Replaced the grinding compound several times. Used a cardboard base. Each piece got one hour and ten minutes of grinding, plus the grind-er got three hours and 30 minutes. They all looked the same and all fit and worked as well as the original. Looks like after an hour's grinding, nothing changes. They can't be judged wet. When they are dry you can see what's going on.
I had a spare I had carried for 25 years in various vehicles. When I opened up the protective packaging.... IT was shattered. Now I have a spare for a spare. Plus another spare.
Turns out the back springs are sprung and the wood that is missing is important. Plus I broke a corner mounting pin off. Looks like its time for a new 5X7 back. I can have one made....for the price of a used 5X7 Deardorff. Currently beating the bushes.
All 4X5 Deardorff Specials come with a 4X5 and 5X7 back. Seems like there would be a few spare 5X7 backs floating around, since that format is used less. It's a scavenger hunt.
But grinding the glass was kinda fun.