MTH, I think the weathering is superb and the sought of thing I'd like to achieve. Any chances of an explanation with pictures?
Easier said than dune........
Always find a good photo of the weathering you want. and try and work out the colours that are in them.
On the Deltic, I use an Air Brush and Railmatch acrilics, built up in layers.
starting off I mask the windscreen wiper path then lightly spray underframe dirt to lower body and bogies, then roof dirt to upperbody and roof area, followed by matt/satin black sprayed out from the exhoust ports then dry brush Greasy Steal around them.
Last but not least spray satin black aroung the axle boxes and spring hanngers.
Hope it helps.......