The most common mistake we see on 1980s-built doors is someone replacing a broken spring without checking the drum and cable it's paired with - on a door of this age, the cable's usually near the end of its own life too, and skipping it means a second failure inside a year. The other one: swapping an opener without checking whether the door's spring balance is even correct first. An opener straining against a bad spring will burn out its own gears trying to do a spring's job, and no opener, however new, fixes a balance problem underneath it. If a door's been limping for months before the call, we'd rather tell you it needs two things fixed, not one, than hand back a door that fails again in a few weeks.