Not sure about Spaz, but Alclad does require a gloss black base - preferably an enamel. Then light sprayed on chrome. I don't think brushing works with these type paints because of the way the tiny particles adhere to the black base. It's kind of like magic.
I have another question - why were you trying to chrome those hubcaps on chrome sprue? I would recommend removing the parts, cleaning up mold lines and attachment points, then primer, base black, chrome.
Black sealer? Is that the black base coat? A dealer sounds like something you put over the chrome...
Enamel base coats allow the chrome paint to "bite" the undercoat and provide a more durable finish. You can get very good results with a lacquer base, but the chrome will be very susceptible to rubbing off.