Scale rot is almost always caused by them laying on moist substrate for too long. Sounds like you probably have a very minor case. Put him on paper substrate (newsprint, kraft paper, or paper towels) for a shed or two. You should see it clear up. You can also swab the area with a Betadine solution as a disinfectant. I would avoid any petroleum based creams, lotions, or magic potions. They all just soften the scales over time.