I just bought a 1986 Ford class C RV with 43,000 miles. I assume it's got a C-6 trans. I haven't looked close at the RV yet or taken possession of it. I plan to do a service on the trans before starting the engine. It's sat for at least a few years. I'm thinking of draining the fluid and replacing the filter before starting the engine. Then warm it up a bit and change the fluid again. Drive it a short bit and change the fluid and filter again to maybe synthetic fluid. I don't have much experience with auto transmissions and I'm a bit worried about the supposed curse of changing the fluid and it kills the trans. If changing the fluid is ok, what fluid is recommended for flushing and if synthetic is ok, what brand is recommended? I'm partial to Red Line oils. How about the rear end, which I believe is a Dana 70 HD dually.