I too have an old Kelty, the D4, that I purchased when I was in High School...many moons ago.
My zippers were stuck and failing, all padding was hard with age, so I called Kelty to discuss. They said, "Send it in and we will fix it for free, lifetime warranty". So I did and they gave me a new updated set of sholder pads, new updated waist belt, fixed the zipper, added a new Kelty triangle logo, etc...
All in all, a great company and worth contacting them for a possible solution.