WD-40 works great for removeing the rubber off the rear quarters, but thats about it. You can try washing off the belt w/ soap and water since WD-40 is water soluble.
Belt dressing dont wurk either. On top of leaving a sticky slimmy coating on it, it softens the rubber and ruins the belt. The only dressing i ever use is a bar of Ivory soap. Run the engine and rub it on both sides. BE CAREFULL. Thats all i can say, the danger is obvious.
Good Luck