Oh dear, that’s a lot of boxes to tick…. Look in the latest (October) Yowl, bottom of page 178, and give Alan Noakes a call. He is equipped to sort out all your sprocket problems, but might need to see the complete back wheel to check on any ovality where the bolts go through it. Don’t try and live with the wear in the bore of the sprocket as that is probably a major cause of your problems. It is important that the sprocket is a nice working ‘fit’ onto the spigot in the hub. Give him a call to discuss it anyhow. He is only in the very next county to you. Sorry to have worried you with the word ‘arcuate’. It really only means arched, or ‘bent like a bow’, but has zillions of medical meanings too !