Well I think this works!

The 3 vinegar tank cars, each with a different level of weathering.
I find silver paint jobs the trickiest to weather. Maybe that's just me.
I started with a wash of black ink diluted heavily in alcohol. That helped pick out the boards in the tanks and highlight the bolts, etc.
I set the one on the left aside at that point.
Then the other 2 were washed with a MiG product, a grey enamel wash which helped add the a level of overall dirt to everything and further highlight the tanks.
Then the middle car was set aside.
The 3rd car was given another very heavy wash of the grey enamel, making sure to build up colour around the tank bands and straps.
Once that had dried, all 3 were oversprayed with suggestions of dust and road grime, the underframes were given a good coat of oil crude and road dirt.
All in all, I'm pleased.
Now to check with the client!