I just ordered a case of Rustoleum Stop Rust Enamal protective paint. (It is ordered by the case in 4 - 1QT cans. Or spray or 1/2 pints)
Home Depot, at least here, can order other colors besided what they carry in stock. I wanted Harbor Blue since it is identical to the factory B1 blue on the Duster now (mostly). I didn't want to have it mixed in store because of the bubbles. Also, I don't know if the dyes they add would affect the paint composition negatively.
I didn't see any Penetrol product though. Poorbugr, did you pick yours up at Home Depot? I'd like to try the Penetrol method if that is really the difference that gives it the adhesion and deep gloss.

Here is the company website for Penetrol (and Floetrol)
http://www.flood.com/Flood/Products/Exterior/PaintAdditives/
Is this the product you used? it appears to be made for thinning oil-based house paint.