Hi,
Nice looking AFV there. Godo clean build. I'm by far no expert on washes, but I usually will start my models out with a wash of Grumbacher's van Dyck Brown oil mixed with about 90% of this company's thinner. I like doing what is called a 'pin wash' effect, I think it's called, where I just use the tip of a very small brush and just touch it to or around any raised detail areas and let the capillary action move the color around. Letting it 'run' into recesses and flow around bolt heads, tooling, hinges, etc. What you're looking for is just that hint of shadow that sort of gives a 3-dimensional effect to all the details on the vehicle. Then if I want a little rust in certain areas, I mix up some Burt Sienna, maybe adding some of the van dyck brown to it if the color of the burnt sienna is to bright, and again just using the 'pin wash' effect to add it where i wish it to go.
After a hour or so I will check to see if there are any areas of the vehicle where the color of the wash has flowed out into the open, so to speak, or into areas that I don't want it in, and use a Q-tip that has been lightly dipped in some of the thinner and squezzed out and lightly go over those areas to remove some of the wash color. Now remember lightly here as sometimes if you happen to rub a bit too hard you can remove both the wash color and the paint as well, which I've done a few occasions by getting a little to phsyical .
Just practice and do a little area at a time and then look it over and see if you are getting the effect you wavt.
Good luck and takecare, Sgirty