I just noticed during some rain today that water seems to be coming into the cab (into my newly repaired cab corner) from the top of the window rubber seal for the back slider window. I intend to replace this window with a newer black one I got at a swap meet last year and install a new window rubber as well. I assume this will stop the leak but I want to know if additional sealant is required along the top and sides of the rubber and what type would work.

 

As long as the body is straight there should be no sealant required at all.

 

I would talk to a local windshield place. I believe they do put sealer in some areas for extra insurance against leaks, but I would ask them to make sure, and they probably know what kind of sealer to use if they do use some.