For heavy weathering I prefer painting with brushes. This MDC C-25 was spray painted first to represent a clean engine, then I made a light overspray with dust and grime for a normal weathering.
But then I went perhaps a bit overboard with dirty washes and drybrushing all sorts of dust, rust and dirt. I find that the streaky appearance of heavy grime and soot is best made with brushes.
So IMO she doesn't only look dirty, but also quite a bit banged up (look at the shiny part of the smokebox!), although the surface isn't scratched at all.
So you even might paint her again als shiny and new if you don't like all that dirt. :thumb:
Ron