S100 engine detailer will make the black casings look like new again, but the spray is about $10 for a can. I doubt you could cover all the black on an 8-ball with one can.
For the past couple of years, I have made my own black restore mix as given to me by a friend who shows bikes. Basically it's a 50/50 mix of Mother's Protectant and water. Mix some up in a hand held spray bottle, and spray down all the black wrinkle finish. Wipe off any extra from chrome, and dab up any "pooling" out of horizontal recesses, and let it air dry while you shine other parts of the bike.
I've used this mix for the past couple of years and not only is it a fraction of the cost of S100, it looks darker, and definitely lasts longer.
Haven't used it on my new bike, but did on my RoadKing. I plan on trying it on the swing arms since they are the same wrinkle finish.
'09 Kingpin 8Ball
'06 HD Road King
'06 Vulcan 900 Classic