I would suspect it's just normal wear and tear on the cush drive bushes, especially if the bike has been used hard on the track for 3000 miles!
You could replace the stock cush drive bushes with titanium and urethane ones. Seemingly last forever and also prevent the bushes "backing out". Downside is they're V expensive and I don't know of anywhere in the UK that stocks them (somebody probably will tho!) but they're easy to get shipped from the US. Expect to pay something like $275/£150 a set. Stock cush drives are approx £50 a set.
Hope that's of some use!
Neil
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