the tech ask you to change the crank sprocket because you need to remove it to change the crank seal. In the event of removing the crank sprocket, you might accidently destroy or you'll have to cut the sprocket for easy removal. Thus you will have to change the sprocket.
I never changed my crank seal because of this issue. (scared to death when I think I will accidentally screw something up). I still have the new crank sprocket with me. hehe....