While Winnebago has some of the best online resources of any manufacturer, they don't go back to 1974. Here's a Minnie Winnie owner's manual from 1996.
They are pretty generic, if you read through this one it will give you good information about many of the features of your RV. For specific appliances and systems, do a Google search for manufacturer and model # followed by the word "manual."
I would think your first job would be to stop the leak in the roof. The wood structure of the roof will rot and be a mold issue if not corrected and dried out. The air conditioner has a foam seal between the underside of the A/C and the roof. If you take off the cover the A/C is generally held to the roof by 4 large screws. Get the seal from an RV dealer or service center.
Any seams in the roof that need re-sealing, Dicor Self-leveling caulk is the RV gold standard. Also seams can be covered with EternaBond Tape, available at Lowes and RV parts places. Don't use silicone caulk, it fails and then nothing else sticks where the silicone was.