This area sits in a cold, severe winter climate, and a door built for 1970s expectations wasn't engineered with that kind of cycle load in mind - repeated freeze and thaw stress on hardware that's already decades old adds up faster than it does on a newer install. That's the honest limitation: on some of these older doors, especially ones with worn track and a frame that's shifted with the house, a spring swap alone won't get things running smooth again, and we'll tell you that instead of doing a repair that won't hold. When it makes sense, we replace the spring and cable set together rather than just the failed part, since on a door this old the rest of the hardware is usually close behind it. For openers, we generally recommend replacement over a repair once the unit is into its third decade, since parts for chain-drive units from that era are getting hard to source at all.