The most common problem we run into on older extension systems is a homeowner or a handyman replacing the spring but not the safety cable running through it. The spring is new, the cable is thirty years old and starting to fray, and now you've got a door that looks fixed but isn't. We check the cable every time, even on a straight spring swap, because on a door built when Italy's median house was new, the rest of the hardware is usually the same age as the spring that just broke.
The other way this goes sideways is skipping the drums and rollers because the spring was the obvious problem. On a track this old, the drums have often worn enough that a new spring won't sit right on them. We'll tell you if that's what we're seeing rather than send you off with a spring that's fighting worn hardware from day one.