I have cropped the photo in post #20 and marked what I think are the cam operated valves in the purge unit. The sensors should then be near these.
The sensors might be microswitches that can be tested for continuity with a DMM with continuity test function and
if necessary taken apart and cleaned. The sensors might also be optical interruptors with an IR emitter and IR detector on each side of a disk, vane or similar, I think these will be difficult to test but you could clean the lenses if such are found on the IR emitters and detectors with a soft tissue paper.
Also check for mechanical blockages of the purge unit. maybe something is stuck in old ink?
View attachment 13684