Interesting, I hate all handles except for cork.
If you don't want cork but are forced to get it, use wet or hand wipes to clean them and remove any smudges and dirt/oils. Then, they sell cork sealer at TW and other places. Cheap.
After they are dry from cleaning, use on of those tiny foam paint brushes to apply a very light coating, then let it dry. Too much will just build up; you need just enough sealer so that it soaks in well, leaves nothing on the surface.
Once a year, even less, is fine. It'll take that dark smudge (dirt and oil) off cork handles, make them last a lot longer.