Then replace it.
It’s generally a decision based on manufacturer recommendations, economic factors and mechanical knowledge…..things just wear out. Even us.
Although a reformer spring can’t be re-conditioned, you and I can be!
In order to ensure that the re-conditioning is the most effective, make sure your equipment is well maintained. Obviously a reformer with once-daily use will need less attention than those found at multi-instructored studios.
Also, making sure that all other parts of the reformer are cleaned with regularity, will add extra life to the springs!