Just went thru this with my 87. 
Side seam @ joint. - many of the screws had rusted out and were loose.  Looked like this: 

There was NO buytl behind the edge rail or inside the seam. At the back and sides the plywood backing had rotted away. So, where the plywood was gone, we were able to get new wood strips in there and installed new screws. Where then plywood seemed good, we just drilled new holes between the existing holes and used new screws. Stainless would have been good, but went back with cad or black oxide coated screws. Figure with new vinyl cover and sealer it should last many years.
Sealer - used some stuff in a white & blue tube the local RV store reccomended. Sticky when it went on, sticks very well, a bear to get off your fingers. Will get the name of it. Sealed only the TOP of the side rails at the seam.
Windows - pulled and resealed them all with new buytl. Will use the same sealer as on the side seam, but not seal the bottom. It's been a few months and continues to ooze.