The random (failed) splattering of the hopper interior has now been treated to a wiping by thinners-dampened 1/2"flat shader. I attempted to keep the wipes vertical because that is the direction water would take any dirt and dust that it encountered. It is quite probable that any effect thus produced will be entirely obliterated by whatever is to follow, but, just in case. . . . . . 

This was followed by an airbrushed application of very thin Railmatch Weathered Black - plenty of thinners and not much paint. The main idea of this was to dull down the orangey tone of the Revell 84.