Perhaps this information is coming too late, even so:
This type of ph meter does not have a combined electrode. Thus, there are two separate electrodes on it: the working electrode (the glass sphere) which is with an Ag/AgCl wire filled with saturated KCl solution, concentration: 3M). And also the reference electrode which is exactly the one you marked in the figure, indicating it with a red arrow.
The reference electrode in this type of pH meter is a silver wire immersed in a POTASSIUM CHLORIDE GEL (3M KCl solution and 1 or 2% agarose). You can see that there is a little gel in which this thread was soaked. To avoid the passage of ions, what comes in contact with the sample to be analyzed is this small white "tube", which I don't know what would be the material of its composition.
It is difficult to extend the life of these electrodes, and soaking them in KCl solution can help. But they "say" that the gel in which the reference electrode is immersed lasts about 6 months to 1 year.
An illustration of a pair of electrodes of this type (those that are not matched) can be seen at: https://www.globalspec.com/learnmore/sensors_transducers_detectors/analytical_sensors/ph_orp_electrodes
And congratulations for the photos of the equipment, they were very good.
3 important tips that never appear on the web about using these devices:
1. In addition to the obvious problem of validity of electrodes, these equipments can give problems due to adhesion of organic material on the surface of the glass. In this case, you can leave them for 24 hours immersed in a 3% hydrogen peroxide solution (10 volumes), it may be that this will "resurrect" the equipment.
2. Another idiotic detail, but very common is that when the batteries are low they can indicate incorrect values, it should be checked before discarding the use of these equipment.
3. These devices are not waterproof, but the problem is much bigger than that - I always see that there is permeation of the solution into the circuit: that is, if you use it frequently, within 1 year (2 at most) most of the electronic components will be corroded.
Sorry for the incorrect English or the translation not being 100%.