There is a gear on a serrated shaft between the odo and tripmeter. That gear will, over time, loosen on the shaft. What I did was slide that gear over to one side, put super glue on the serrated area and slide the gear back in place. What causes this is resetting the trip meter while the car's in motion. The gear eventually works loose on the shaft. Try
www.dieselgiant.com for the write up.