Hi michael, thank you! I'm extremely happy with the results myself.

For the oil splatters I mixed up a strong wash of black/paynes grey/raw umber oils and with a very fine brush applied where I wanted the dark stains. Then on top of that I used some thin tamiya soot paint. It gives the wet look to stains.

Then I mixed up a thinner wash out of different browns and loaded it on a brush that I splayed the brush fibers to flick wash drops randomly. Do that from various distances to keep things random.

As for the dust I've just been reading and rereading the tank art series and this is my 4th attempt at recreating the dried dirt.

As Mr Rinaldi suggests mix the pigments like paints (dry of course) so mix a base color (I used 6 different colors to mix this I think) a highlight color and a shadow color. I apply these with the model on its side letting the pigments fall from a brush above the model.

Once your happy with the mix, keeping it random I use a medicine dropper with 99% isopropyl to fix the pigments in place then drying with a hair dryer to speed things up. I also add more pigments to the wet base where I feel necessary and did this in 3 layers building up the pigments and colors. Then I applied oil stains just like on the road wheels.

Hope this long winded response helps.

Cheers
Jon