Unfortunately pH Probes do not last forever as they age through normal use and will eventually fail. With good care and use (keeping the probe tip wet and cleaning once a month) you will extend its life.
 
The Bluelab pH Probe has a double junction reference which provides a longer life than many other pH probes and is a gel filled non-refillable probe, so apart from cleaning is maintenance free.

• Double-junction probe reduces reference contamination, extending longevity  
• Fully waterproof - not just water resistant  
• BNC connector allows use with all other compatible Bluelab products  
• 2-metre cable for measuring in hard-to-reach locations 
• Use the included storage cap with KCl to lengthen probe’s lifespan 
• Fast sensor response ensures quick and accurate measurements  
• Polycarbonate housing for long-lasting strength  
• Effective in solutions of 0.2 EC and above