I'm not sure what model you have, but I've heard of similar issues with the 850. It is most likely the small 7mm diameter gear inside. So you need to remove the instrument cluster per Bay13 instruction and take the odometer unit out. Once you did that you need to remove the motor held in place with two screws shown in the picture and replace the yellow gear. Then read the milage from your ECU (explained on this site or dealer can scan it if you do not know how to read it) and match the mechanical odometer to your REAL milage!