I must say , out of all the heat paint that I've used I like Duplicolor the best, always use a hairdryer when painting, cook it with a hot hairdryer for about 20 mins.after paint has set up, had no problems. It's paint, it either flakes off with poor prep,looks old because of use and age, That's the nature of a cover coat,so don't skip on the prep,put enough paint on it so it will last and look good longer, and a hairdryer to stop drips.
My favorite color for stock engine is cast aluminum .secondary color choice aluminum, jugs either cast iron or semi gloss black. The flat black seems to be the weakest of the duplicolor line and some bar b cue paints will prove to be more durable.
Painted this last week or so
aluminum with cast iron jugs
works for me.