I (well, my landlord) replaced a similarly old refrigerator last year. The thermostat was fine, it had developed a very slow gas leak and the charge had dropped

I (well, my landlord) replaced a similarly old refrigerator last year. The thermostat was fine, it had developed a very slow gas leak and the charge had dropped enough that it was freezing rather than cooling. It was using around 29kWh/month before the leak was noticeable, the new one uses 12kWh/month. The new one is slightly larger than the old. The old model was freezer-on-top style, the new one is a less efficient freezer below model. Hopefully the new one lasts as long as the old!