The rubber had perished on the sides of my pocket knife, so I cleaned it out. The original rubber came out with just a fingernail embedded in it, and the same fingernail served to clean out most of the glue. I cut leather to size with a scalpel and glued it in, smooth side down. Then I shaved off everything that stood up. It’s matted down a bit, which is not hugely pleasant to look at, but it’s comfy to hold, and I think it’ll wear to my hand eventually. If not, I can always rip it out and start again.