Ah there you are - I was trying to remember who it was I read about who had taken on the manufacturers and won on this, I just remembered you had that caravan cartoon avatar!! - Perhaps the OP could dig it up as if I remember rightly it was pretty lengthy and they could probably pick up some useful tips.
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Please note that it was my dealer I had the success with and not the manufacturer as your warranty is with the dealer. What agreement he comes to is between him and the manufacturer, who in my case supplied the parts free of charge as a goodwill gesture, if you believe such rubbish!!