If it dry then it
U can calibrate it again. Crazy old man
They don't need a lot of solution to stay wet, but they do need to never dry. You can always try to calibrate it and try it out. If it either doesn't calibrate, the PH on the controller is way out of wack or it shows massive swings, it's toast. It's worth a couple bucks in calibration solution just to give it a try. I used to chase PH numbers but now I only keep a probe in my tank to shut down the a Kalk reactor if it malfunctions.
What else you got growing in that tank. Heh.