I had noticed a crack in the sprocket cover so I had a spare cover polished and today I fitted it.
Of course, nothing is ever straightforward as the collector box stopped the cover being removed. And in order to remove the box I had to remove the whole exhaust system. Unfortunately I was unable to save the new gaskets so I had to fit 2 new ones again. It was an easy job, and then I had to refit the whole exhaust system.