My grandpa had maybe two dozen Rivarossi locomotives he kept on display in his living room for more than twenty years. He was a prolific smoker to say the least and these locomotives became very dirty over the years. A few months before he died, he purchased the Rivarossi "1930s Super Chief" passenger car sets to match his twenty year old Blue Goose locomotive. It was immediately obvious how much damage had been done to that and the other locomotives when the new blue cars were held up next to the grungy old blue locomotive.
I inherited the entire collection and after some time had passed, I decided to see what could be done to improve the appearance of some of these locomotives. The first thing I did was disassemble the Blue Goose and separate the parts that could be immersed in water from the electrical parts. I dunked the shell into a pot filled with water and scrubbed with a toothbrush. I tried a number of different cleaners before trying out some orange cleaner (can't remember the name, maybe "Citrus Magic"?). The built up cigarette smoke crud was removed easily when nothing else worked.
Of course, the locomotives I applied this cleaner to were factory decorated, so I suspect they'd be less susceptible to damage as opposed to custom painted and decaled models. It's a good idea to test any cleaner before using it.
As for the running gear of these models, I simply clean everything out and replace the lubricant with a minimal amount of Labelle oil and grease where appropriate.
