In addition to clearing my own backlog I’m also dealing with some items from friends, including these n gauge locos. The techniques are essentially the same for locomotives in all three scales I have weathered, but you can see that the overall effect is the same regardless.
Anyway, I probably don’t have to say too much beyond identifying the class and make; the photos can do the talking today, I’ve got heavy work upstairs to be getting on with! 😬
Max Stafford's Kennel 
Nice. Any scope to make the coal loads in the tender of the A2 and A1 less of a “mountain”? Or is it that shape because of the innards? Looks like for the A1 there is some real coal on top? If so the plastic look of the A2’s load highlights the difference that change makes.
I believe the motor makes that heap of coal necessary in the same manner the old Hornby tender drives did in OO, John.
Ah, though that might be the case, but I am not “up” on current N gauge models. I had in my head they had moved back to loco drive! Maybe the A1 and A2 are older models, although they look the part, especially with their new coat of weather.