It's always hard to get the right colour shade from old photographs as they look very different in every picture
you look at. So in the end you have to pick one.
They were always dirty so all you can do is get the brown paint out.
The bright yellow finish on the plough van is hard to get it darker.
It took many thin coats and dry brushing, you can't do it all in one go.
Sometimes i had to wash it off and try again, not easy. Now i have to do the other one.
It took a lot of work to get the right effect.
It was built up with brown enamel then varnished and dry brushed with more brown
and Humbrol rust powder, then varnished again.
I had a problem like that once with a Bachmann railcar.
When i opened it and had a look at the drive from the motor there was a very small piece of plastic catching
as it spun round so i cut it off and that cured it.
I don't know how much you can see with the cover off but have a good look inside when the motor is running.
you can slow it down and try using a magnifying glass.