I'm not sure about your specific probe, but we (at my lab) store all our pH probes in KCl salt solution. The working life of our probes is 2 years or so, and that's with daily use.
We use Calomel glass probes. They have an internal solution that is easy to fill and maintain. So of the other electrodes that use membranes may actually leach internal filling solution into the solution being tested.