I have a Chorus 10 spd cassette with about 3,000 miles on it. One shop said I might want to replace it since I just got a new crank. Another shop said it looks fine and don't bother. So what is the normal life span on their cassettes? I spin more than mash the big gears, but there are plenty hills here. Admittedly, I wasn't the best at keeping my old chain clean (changed my ways after snapping one on a climb and shelling out $55 to the LBS -- chain = labor).