The previous tip about the baking soda is righton target. After the baking soda clean the board with alcohol or some sort of contact cleaner. Not tuner cleaner as it has a lubricant. The coating on the board ( called a conformal coating) is either polyurethane or an epoxy resin. If you want to recoat there are conformal coatings in spray cans available from electronics supply houses. I repair boards regularly without replacing the coating though.
Hope that helps.