Hobby Hint
Here's a nice way to go about weathering all your model trains. Go to railroadpicturearchives.net and you will find the road numbers of all the rolling stock in the United States...
Click on the style, (brand), of rolling stock, i.e. ACF, then the road number, and you can see a picture your piece of rolling stock exactly as it appears today, (graffiti and all). Enlarge your picture and print it out.
You can see wear patterns, dirt marks, road grime, and rust spots. It is an excellent way to weather realistically using the existing piece of rolling stock as a template.