Thanks mate.
I sprayed light coats of gunze oil and smoke over the dirtiest areas and copied Ray Rimmell using a post it note moved along the under fuselage as a mask to put muck where the formers are.
Then I dry sponged polyscale mud on with a scrap of sponge
Finally a tamiya small qtip soaked in cellulose thinners was used to focally wipe bits away. I Also brushed on dollops of oil and streaked them in the airflow direction.
The effects are used less and less as you move away from the under engine.
Key point is study a photo and use focal point weathering rather than global effects.
