On a house from the late 1930s or 1940s, the spring is rarely the only thing we're checking. Cold-climate winters put real stress on steel that's been cycling for decades, and this region sits in a severe cold band, which shortens the working life of springs generally and makes brittle fracture more common on older coils than on newer ones. We check the drums, the cable condition, and the center bracket before we call a job a clean spring swap, because on a door this old, the spring is sometimes the symptom and a worn cable or a cracked drum is the actual cause. Honest limitation: if the torsion tube itself is bent or the drums are the wrong size for a modern spring, we'll tell you that on site rather than force a part that doesn't fit, and at that point you're looking at more than a spring repair.