The optics point up on the joystick and the crud pointed out in the link above would fall on the optics and cause the stick to not function correctly.
Actually, no the optics point DOWN (the reflective disc is _under_ the optics PCB) so the crud story is a myth. I think it was much more a case of the reflective disc becoming dirty (dust, crud, drink spills maybe) or maybe the actual optical parts becoming bad (looks like one is replaced on mine).
AND I think the basic design is not that great. Hitting the diagonals is hard and is essential in the later stages of the game (so far scored just into the 10000 points).
I released the spring as much as possible because it took a lot of force to play a game. That is already much better (you'd expect a spring to loose some strength over the years but this one is still very much alive).
I even thought about removing the spring completely.
I do wonder about that crud under the actual handle. If that used to be a rubber disc, it would "soften" hitting the end of travel on the joystick, which now is a mean "hard" bump.
The drawing in the schematics do not specify it though....
They do specify a spacer (nr. 3 on the drawing and list) but it doesn't say what material it is. I haven't _fully_ disassembled the stick yet though. It's all pretty stuck.
I am going to experiment with a Suzo Inductive joystick base. If I could get it to work with this joystick it would be the perfect replacement.....