I have a customer that comes in once or twice a year because his VERY OLD quartz-driven Seiko "Just started running backwards."

Turns out the rotor on the stepping motor had two magnets, that were independant of each other but fixed to the same arbor. The great inertia of the rotor stopping and starting once a second would cause one of the magnets(which was slightly loose) to shift enough where the watch would impulse backwards!

Seiko discontinued the part long ago, but he comes in and I fix it long enough to get him another 9 monthes to a year down the road.

Chaz