Both wires and terminals become brittle through age and vibration induces work hardening. Failure normally occurs near terminal ends without warning.
Stainless steel wire, unlike galvanised does not fray and the inexperienced eye would find little difference visually between a sound stay and one that needs condemning.
For your own peace of mind, why not have your rig professionally checked.
We will make a visual inspection of your Spars, Reefing Systems, Standing and Running Rigging and Lifelines. A report will be submitted advising if any work is required to put your rig in first class condition next season.
An estimate for the work recommended will be sent to you.
Even if no work is required you will find our report useful when in correspondence with your insurance company.