Welcome to the forums. We have a 79 Sovereign
as well. The window gaskets that were used (if original) is a double lips type and the experts say there is a newer, better seal to use (the 'D' gasket). We also used the same gasket for around the door frame on ours and it has been a year without leaks.
Here is the link to Andy at InLand RV explaining the type to use (you can also order through him):
That forum also has the process for replacing I believe.