goel-370 oxygen sensor failure

[dinogep]

Two o2 sensors in our dive group started acting strangely. Both are GOEL-370 sensors, used in GOX-100T analysers by Greisinger Electronic. Both sensors are only half year old. The symptoms are: after switching on and calibrating the analysers the output seems to be stable at 21%, but changing the position of the sensor (turning it upside down) makes the displayed percent value decrease to ~16%. Turning the sensor back makes the percentage go back as well). In the past year I have using my sensor I have not noticed any similar behavior, nor my friend using the other one. The position sensitivity makes me think of some liquid changing position in the sensor (e.g part of the electrolyte has disappeared), but what could cause this condition? The sensors when not in use were stored at room temperature, with closed plastic cap.

thanks

Dino