There is no potentiometer in scroll wheel, it use encoder instead. First you need to open and clean it. Usually encoder is an optical device and sometimes small derbis, dust, hair can cause malfunction.

You can use for contact cleaning some solution. I prefer (it is avaiable from local store) Cleaner KONTAKT 60 by KONTAKT CHEMIE. You can add some acid to it if it is a strong rust vinegar or lemon juice. Don’t forget to wash out acid. For washing electronics I use isopropyl spirit rather then ethanol. As for rubbers I prefer not to use any because you can easly scratch electroplated layer of nickel, and then oxydation occurs much faster. BTW, I don’t know about your camera, but my canon accepts batteries with some special chip only. Otherwise it can’t show level correct.