I take it your retailer was a UK dealer?
Assuming that it was, then in British law, HE is 100% responsible for addressing your problem and well he knows that! If the goods are clearly faulty, and from what you say, this seems beyond doubt, HE must repair, replace, or offer a full refund, INCLUDING the shipping in both directions. Which of these actually happens is subject to negotiation between you and him. But what is absolutely CERTAIN is that he may not, in law, pass the buck to anyone else unless you agree to it. So don't! As for him 'bending over backwards to assist' you. From what you say here, he appears to have done absolutely nothing - other than give you an address to pass the buck to and avoid facing up to his own responsibilities!
I have experienced similar situations in the past and have always found that a very clearly written letter, describing the situation AND the legal obligations, politely but extremely firmly has, without fail, produced results. I haven't had to do it often, but have always had success when it was necessary
I don't know how our board Admin feels about this and I will of course respect his wishes, but it would be very interesting to know who the retailer is.
I would strongly suggest you make a careful and accurate note of dates - when you made the original transaction, when the fault was noticed, when you contacted whom (and by what means), when you returned the goods, when they were returned to you, everything that is relevant, including all the costs incurred in re-shipping.
Inform the retailer that you have done this (in fact inform him even before you start!) and that you have every intention of following through to the maximum extent of the law. Be polite, but convince him beyond the tiniest shadow of a doubt that you will NOT let him wriggle off the legal hook. Tell him VERY clearly that if he is unwilling to settle the matter amicably and co-operate, then he will also become liable for all the additional expenses incurred in obtaining your legal right to satisfaction. Inform him very clearly that his responses to your request are being recorded and that, if his refusal to assist makes it necessary, his refusal to co-operate will be used in evidence against him. Remind him of the damage that WILL occur to his business reputation should it become necessary to take legal action.
If you still cannot gain satisfaction from the retailer, then do NOT give up - never give up!
Telephone or write to your local Trading Standards Office, which are there to ensure that retailers comply with the law regarding sale of goods. It's one of their prime reasons and purposes for existence. It may be necessary to contact the dealer's local Trading Standards Office, but your own Office will advise on this and probably assist you in doing so. You may wish to contact the Citizens Advice Bureau for further advice. But do NOT give up!
As for "Fleischmann UK", I am not sure that they are in fact owned by the Fleischmann company. It is possible that they are, but perhaps not and have simply negotiated the right to use the Fleischmann name, in UK, as Fleischmann's representative/distributor to the trade. It would be useful if this could be ascertained for sure. Does anyone here know the answer to that, please?
Regardless of that, your dispute and its redress is technically with the retailer and no one else.This does not prevent you from negotiating a settlement with Fleischmann if you and they are both willing, but it is usually simpler to deal with your known and presumably English speaking retailer.