Yesterdays experiment with the Venetian Cream worked out well. At least the bellows didn't fall apart during the night. So this morning I continued to treat the rest of the bellows. See the before and after pictures.
After that I touched up the wood where it was scratched with a furniture touch up pen. If you are going to do this on your camera, don't forget to wipe off the ink immediately after you applied it. Don't let it dry on the lacquer around the scratch. Just wet a tip of a finger with some spit and wipe the ink off.
Next I put the parts together again. This is the result. (Photo taken with smartphone. I hope to take some better ones during the Xmas holiday.)