Just a fyi friends. Although I sold my Mav a month ago, it worked flawlessly for the prior 4 years. I had opto issues in the beginning. Took every one off and reflowed the solder on every joint. Opto, resistor...I reflowed all. Never had an issue again. Did my Judge Dredd also.I remember specificaly one opto moved just teeny weeny back and forth on the pcb board. All so small a distance...could not see with eyes but fingers felt the movement. My point is obviously that one must not have been a good connection. Theses solder joints get micro stress cracks in them over time. All the items, usually, on the pcb board are actually fine...just that cracks developed and then Bam! Intermittent opto issues because electrical continuity is not consistent!
If you obtain used replacements (heck, even new) aI suggest reflowing the solder just to be on the safe side.
Merry Xmas!