Most of the nuts came out with minimal force, but the last one just spins in place. I tried rubber gloves, painter's tape, and duct tape to get a better grip. I'd rather not cut a slot in the domed nut if there's another good strategy.
The rest of the restoration underway:
It's the nut recessed? If not, you can use a splitter on it.
https://upload.wikimedia.org/wikipedia/commons/7/72/Mutternsprenger_0610.jpg