Did you try cleaning the opto?
Replacement board
https://www.marcospecialties.com/pinball-parts/A-15894
Quoted from underlord:The best I’ve seen and have though are the Great Lakes modular opto-less boards. Amazing work on these. If you can find them.
I have these and absolutely hate them!
The small magnet is very hard to adjust, thay vibrate out of adjustment and I smack the flipper buttons pretty hard and thay vibrate so that you can feel it through the button. I just hate them! I finally replaced them with complete new boards from Marco.