Yah, had the same thing on mine. There's a short little cable that runs in a tight arc from the reset knob thingee to the back of the odometer housing. I think it just fills with water / condensation and then eventually gives it all up. I detached both ends and bathed the thing in WD40, then dribbled a light machine oil down it. Since then, it's been fine.
Hey, thanks.... That's what I thought, but I didn't want to pull it all the way a part with out a little more info. The parts diagrams just show's it coming off the back of the speedo (no indication that it actually detaches or anything).