I broke open one of my proto 2000 40' stock car kits yesterday and immediately noticed that the trucks needed some serious help... Here is what I did: I mixed flat black, flat gray, burnt sienna, and rust with some medium gray weathering powder. I painted the entire truck, sans primer (which is probably why I got the purplish effect at first.) which gave it a nice rusted texture. I then mixed flat black and a small amount of the weathering powder to dry brush grease details on the fire box, king pin, and the suspension. I then used the weathering powder by itself to add a road grime effect, then hit it with dull coat. I did not dilute any of the paint. I am fairly pleased with the result. The car that this will be mounted on has a built date over 20 years before my prototype year. Note: They don't look that purple in 3D.