Inexplicable wheel grime?

[Green_Elite_Cab]

I don't want to shoot down the club for dirty track to much. They do regularly run the cleaning train around, which has several of the heavy duty brass CMX cars. These seem to do the job pretty well. As I understand it, I was one of the first locomotive to travel over the tracks after it was clean. Its possible that it got extra dirty over a short time span, but that wouldn't explain why this locomotive is the only one collecting dirt at this rate. Even other engines of the same class (AEM7/ALP44s) were not experiencing any trouble.