Simple Green is how I clean oil and old crud off my machines. Works great. Once in a blue moon I’ll bust out the brake cleaner for a stubborn spot of old cosmoline or something, but it’s rarely needed. Acetone is also a great all-around degreaser. For thicker more stubborn stuff, there are a number of automotive degreasers that work great that are still a lot milder than brake cleaner, so check your local auto parts store as well.
For removing old paint for a restoration, try Citrus Strip. It’s great!
