Jeff,
There are a number of methods I use to clean and preserve original paint.
I use used fine grit sanding disks from a local auto body shop, steel wool,T Cut (a British product that you have to go to the UK to get) and a mixture of used hydraulic oil, used Chevy engine oil (from our 3/4 ton truck as it never gets very black) and Diesal to preserve it after cleaning. You have to experiment and be very careful not destroy what paint you have, a tractor that has been repainted at sometime in its life can be a lot different than factory paint. I have a lot more fun doing this than repainting.