Powerbook 145 Rollerball only working vertically

[Spode]

Hi!

Got a 145 I'm restoring. The rollerball works perfectly vertically but horizontally it's erratic at best, but mostly not there. Opened it up and as far as I can see it all looks good. There's no sign of debris on the spoke wheel that might cause things and I'm not sure where to move next. Are those emitter/sensors prone to dying?

 

[Spode]

I've managed to solve this - so putting what I did here in case anyone else has a similar issue.

Unfortunately I couldn't tell you which did it - but I touched up the solder joints on the sensors for the horizontal and then I sprayed contact cleaner into the ribbon connector and that seemed to do the trick!