I removed the front tire this weekend 'gently', swapped out the punctured tube, remounted etc. and started to ride again straight away. Within minutes the ABS solid light was on indicating that the system was 'off.' Pulled over on the side of the road (night) got a flashlight going and saw that the black plastic sensor was actually touching the rotor. After further investigation it seems that the last owner never replaced the left side axle bushing which served as a spacer for the sensor.
I tried loosening up the axle tension just enough to get the ABS sensor some distance, and it worked for about the next 24 hours. This morning on the way into work it was back on again, telling me in angry red letters that I still have a problem.
Anyone have any tips on this? Will be getting that bushing asap but really don't want to replace the whole ABS sensor component....