Cable and drum failure cascade
Thirty years of cycles later, a spring that's still original is well past its rated life, and it usually doesn't fail alone - the cable on that side stretches or frays under the sudden slack, and the drum can walk sideways on the shaft. If only one spring on a double door goes, the opener will often still try to lift the door on the remaining spring, which stresses the gears and can crack a plastic drum faster than the spring failure itself did.
