I usually take the drum off several of the winches every few years and you can get a sense whether you need to go further. Often, especially if they're in a protected area on the boat, you don't have to do anything. If they've taken seawater over them I always do an inspection at the end of the season to see if it's gotten into the internals at all.

I can do all the winches in day. Mineral spirits and toothbrush to clean things up, let the parts dry, then reassemble. A couple drops of machine oil on the pawls (and definitely no grease on the pawls) ... Then a very light coating of grease on the bearings, teeth and the like.