The insides on the cluster came apart (little gears on the odometer). If you remove it and take the cover's off, you may be able to repair it. It should be an easy task compared to your seat motor job....or was that Bud?
I know the trip odometer works a little bit weird on my 95 with 160k on it. It doesn't always reset to zero properly. Sometime I have to reset it and then drive for a mile or two and reset it again.