Thanks very much!

It's brush based, I tap the tip of a pointed brush in the unthinned paint, dab it a few times to take off most of paint then start tapping the model. The sequence of colours was: I used a chrome first, to look like the border of where the paint comes off the metal and can be exposed to be able to rust. This marks the extent of the chipped area and other layers happen inside that. The second layer was a black brown which again I used the pointed brush for, leaving some of the chrome sticking around the outside. Then repeat that with the orangey light rust colour. This time I took the edge off this bright colour by using a wider slightly damp brush and pulling the paint back a little. The next step is the start of staining and streaking, I used a pointed brush to apply thin orange rust colour, under my chipping to look like rusty water around the chipped area. Last step is the streaking proper, I applied a thinned light orange rust colour with drying retardant (I used acrylics) with a wide slightly damp brush to start the streaks. Other streaky bits were done with an orange wash.

I got all the colours in a kit from Vallejo, but they are just selections from their general range. There's a handy guide to the technique in the box.