I had a dud Clayton from Hattons -- they've written to tell me the new chassis is in stock and attached a link to the Heljan "how-to" video.
I replied that I don't even own a soldering iron, so what should we do? I mentioned again that the goods were clearly of unmerchantable quality, so should I simply get a refund from them.
They have already replied telling me that of course they are happy to fit the replacement chassis for me, and I should post it 2nd class back to them, making sure I get a "proof of posting" slip.
From that experience I figure they are on the case, but maybe have too many customers to deal with very quickly. I certainly wouldn't give up, though -- you have paid for a working model and you should either have that or a full refund. Good luck!
Paul
PS: I have also received one of the new batch of Claytons -- very smooth-running and very quiet (the original ones that didn't expire sound like a bag of spanners and take time to "warm up"). Delightful! If only the original batch had been like that. Still, it gives me confidence for the forthcoming BTH Cl.15.