Nothing beats the 'stealth fighter' my winter beater el cheapo honda! BTW thats House of Wal mart Tremclad $12 per gallon
GoJo hand cleaner, scotchbrite pad and a good rinse job works wonders on white primer/suede. On black I would try it in a small spot first to see how it turns out.
whenever my plymouth gets some dirt, scratches, marks of any kind,,, i get out the flat black spray cans,,, and i paint over it,,, she always looks good,,,
I thought WD-40 had silicone in it, and you didn't want silicone anywhere around something you were going to paint latter. Unless of course said silicone is safely contained in a wife or girlfriend.