I have been working on the rear windows most recently.
One of the windows had a definite water leak, and the water from that leak is what ruined the street-side rear corner area of the bus.
The first picture shows the damage on the driver's side, and the second one shows how the windows are installed - the glass is held in place with a rubber gasket between the body of the bus and the window glass. The rubber on two windows is cracked and very brittle. On the third window, (the drivers side rear window) the gasket is different than the other two. It is still pliable, but is a little loose and this is where the water has seeped in. It is obvious that someone tried to seal it with silicone sealant, but this is not effective for this application.
I used a chisel to carefully remove the brittle rubber.
The glass all came out without breaking.
The paint on the inside has unstuck from the steel in some places. Also, you notice that there are an inside and an outside body panel spot-welded together. They are not the same height! This means that part of the body is thinner than in other parts of the window. I am going to weld a bead along the top inside edge of the outer body panel to make it thicker. I will grind it down since my welding leaves something to be desired. I also plan to coat it with epoxy to make it smoother.
So far, I have welded, ground, epoxied and sanded the metal clean. I have primed and painted both the inside and outside. I removed the aluminum strip from the outside which was below the windows and am polishing it up before re-installing it. Always lots of cleaning and polishing work available on Retro!