If the door you've got is original to a house built around 1970, you're looking at a single-layer steel panel, a standard-lift torsion spring, and track hardware that was never built for a 50-year service life. Sagging in the middle of the bottom panel, a door that's noticeably heavier to lift by hand than it used to be, or daylight showing around the bottom seal in winter - these are age symptoms, not damage from one bad event. None of that means the whole system needs replacing on day one, but once the steel itself is pitted or the panel's bowed, patching the spring or track doesn't buy much time. That's the point where we'd tell you straight that replacement is the better spend, not another repair.