Black exterior trim pieces streaky?

[myteg]

I was detailing a ford explorer the other day and I was detailing the exterior trim pieces when a problem occured. On some pieces of black trim, I suppose because the material was different, when I applied Vinylex to make it look nice, it was very streaky and made that trim with that material look crappy to be honest. It looked like oil streaks all over it. All the side mirrors, black trim between windows, and black trim around windows was real greasy looking but the body door mouldings, front bumper rubber pieces, and door handles looked great when I applied Vinylex. Once I applied it, I could not remove it with buffing with a towel nor did adding multiple coats of Vinylex make it look good.

So my question is, is there a certain product that needs to be used on such exterior trim pieces? I want something that helps brighten up the dullness of the trim and not all greasy/oily looking. Why do certain exterior pieces look this way when I applied Vinylex?