Here are the other 2 boxcars I did some work on.
The CP one was bought at the Chicago meet earlier this year so when I tried to remove some of the weathering with a wet with water cotton bud, it also started to attack the paint work, although now looking at it, it kind of looks realistic.
That wasn't a problem with the BN cars as they are factory ready to run, water was pretty effective at removing the weathering, I think you need to do it sooner than you would if you were using enamels.
Then I added some rust to the CP car