On a door this age, the spring is almost never still the factory original - torsion springs are rated for cycles, not years, and a door installed in 1979 has had four decades to burn through more than one set. What we usually find instead is a replacement spring sized wrong for the door's actual weight, put in by whoever did the last repair without reweighing the panel.
Tracks from this era are steel, not the aluminum you see on newer builds, which is good for durability but bad once rust sets into the mounting brackets after enough seasons. Our mild coastal-influenced climate here keeps the metal from the kind of freeze-thaw damage you'd see inland, so when a track fails it's almost always wear or a bent section from an impact, not weather. We'll tell you when a repair makes sense versus when the door's old enough that replacing the whole unit saves you a second call in a year.