You need to pull the cluster out, disassemble it, remove the stepper motor for the odometer, replace the little gear that is stripped out, put it all back together. Look here:

http://www.volvospeed.com/vs_forum/index.php?showtopic=8398

Whether or not you can repair it is up to you, but it really is not that tough. Although you can charge what you want the guy marketing the gear is a bit of a gouge. I get the same gear for half that price and if I take my odometer heads into my local speedo shop the guy will install, inspect, check calibration, and stand behind his work for a whopping $25.00!!! If I did not have to drive over there everytime to get one done I would have him do every single one that comes into my shop.