I've been struggling for ages with the rear wheel skipping and jumping around on my Canon 70d. I'd given up and thought it was probably not worth the repair costs. However…. I bought some wd-40 specialist contact cleaner (not the regular wd-40!!), took the battery out and gave the surrounds of the wheel a good spray and spun the wheel. I left it for a couple of minutes to evaporate and lo and behold it's fixed! Why didn't I think of this two years ago.