You have to replace the full anti roll bar, it's an expensive job in terms of labour as the anti roll bar runs across the top of the chassis as opposed to underneath. I have a knock on mine aswell and looked at getting them changed but I was advised not too as it might not solve the
problem, I've had the knock for over 2 years, it's never got any worse. I've changed shocks, springs, drop links, only thing left was to change the arb bushes, I've also heard it could be the steering rack.
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