[yellow916]

I just spent some time in the garage cleaning the chain and sprockets on the 916, and noticed some side-to-side movement on the rear sprocket. I don't remember seeing this before, so I guess something is wearing; there's no sign of metal flakes anywhere (yet?). So:

How much movement is acceptable?
What is the likely cause?
What are the options (and cost) for rectifying it?

Thanks in advance

Andrew