Ultrasonic Cleaner Solution Recommendation / Cleaning Athearn Metal Freight Cars

[ai5629]

I am currently trying to get some Athearn 53' 6" GSC flatcars ready for paint.  I am repainting these for a third (and hopefully final) time, and I really need the paint (SCII) to stick and hold up to decal setting solution being place on them.  I have removed the paint with Klean Strip premium stripper and after wash.  The issue I am having is the casting appear to have oxidation on them.  My concern is this will affect paint adhesion.  I have cleaned them with Scalecoat wash away followed by Dawn dish liquid in an ultrasonic cleaner, and they still appear slightly oxidized.  Is there a cleaner that anyone can recommend that will remove oxidation on Athearn cast metal freight cars?  It does not have to be used in an ultrasonic cleaner, but that is a bonus.  Thank you in advance for any recommendations.

Jeff

[rodsup9000]

 I always wash metal items with TSP (get it at Home Depot). I don't know if it'll take the tarnish off, but it's pretty strong stuff.

[wvgca]

TSP by itself is pretty strong, also a wash of pickling [or household] vinegar will give a little bit of an 'etch' on metal to help hold the paint on .... a coat of primer is preferred, as well as a bake later on ..