Hi Craig
I have had similiar problems with the sensor adjustment, but inside the sensor arm i have repositioned the bulb closer to the lense. It seems that the end of the arm the small plastic part with the legend on opens easily and can be slid out far enough to carefully reposition it.
The tone arms tracking to the centre I have experienced problems with this but adjusted the sensor and it has stabalised the motor and the arms tracking movement.
I hope this makes sense.
Cheers
Kevin