First thing on site, we check whether the spring, cable, and rollers are original to the house or a prior repair. On a 1980-era house, original is still the most common answer we find, and it tells us the rest of the hardware - hinges, the track, the opener's internal gearing - is probably original too, even if it hasn't failed yet.
We replace what's actually worn, not the whole system on principle. A snapped spring gets a matched replacement rated for the door's weight, not a generic size. A grinding opener gets diagnosed before we recommend swapping it - sometimes it's a worn gear kit, sometimes the motor itself is done and a new opener is the honest call. We balance the door and test the auto-reverse safety function before we leave, since that's the part that gets skipped on cheap jobs and matters most with kids or pets around.