I think the best place to start would be to remove anything on the roof that would give you access to inspect the type of construction. If it has roof air conditioner or covers and frames for ceiling fans you could remove one and exam the cross section of materials.
More than likely a rubber or aluminum outside skin followed by a layer of plywood, followed by a framework, either metal or wood (more than likely wood based on vintage), which will have insulation, followed by an interior sheeting and finally an interior decorative surface (different types based on vintage). When you see what you are faced with, you can decide how to proceed with either complete replacement or spot repairs.
If spot repairs will suffice, you can then just clean, re-caulk and re-seal everything that passes through the roof and possibly replace the top surface and interior decorative surface. You can do an Internet search for material to finish the roof both exterior and interior.
Here is a link for a brochure on your 1973 Chieftan!
http://www.winnebagoind.com/products...eftain-bro.pdf
Good Luck!