I have pretty good luck cleaning models with a soft brush I found in a dollar store. I think they use them for makeup like eye shadow or something.
Bigger problem I'd occasionally seen is when dampness discolors parts of a ride, particularly paper or posterboard parts. Repainting or reconstruction is the final solution to that one. I remember repainting a scratchbuilt Scrambler the night before a big show.
Model maintenance is much like running a real show. Cleaning, painting, relubrication, rebuilding.
Now, we could get into the cat stories too. I have a few of those that some of you have already seen.