I don't really get this I am afraid. If a manufacturer sells through third parties why is it different if one of them uses Amazon as a platform for sales? If the manufacturer supplies to any third party there is a risk that reseller may cause an issue with their product. Why is it a unique and different issue when something is sold via Amazon or Ebay? I could understand if the email said something like 'you must go through the party you bought it from and they may contact us', that is reasonable the consumer's contract is with the reseller and the reseller's contract is with the manufacturer. It is the implication that had it been bought somewhere other than Amazon or Ebay Yukon would have helped, but as you went via Amazon 'tough luck' I think unreasonable.
Because the barrier to entry for resale on Amazon or Ebay is SO much lower. They try to make sure they have good, reputable resellers on those sites (especially amazon. You wouldn't believe the hoops you jump through), but really, an email address and probably a warehouse for inventory (could just be a closet in your house). There isn't a brick and mortar requirement. There isn't a "public facing" storefront that needs to be maintained. That stuff isn't important to online sales, but maintaining those things brings about a certain level of trust with a consumer and as a business operator, you learn how to manage consumers properly (or your business fails).
Yes, there is risk with any reseller. And really, what you put in your response, "you must go through the party you bought it from and they may contact us" while being worded better, is still kinda telling the consumer to piss off.
Another dirty little trick that resellers will play is buying at wholesale and reselling below MAPP (minimum advertised product pricing). OEM's try to control their prices (though, technically, in the good ol USA its called price fixing and is illegal) so as to not cheapen the brand. Its common to have MAPP somewhere in the neighborhood of 20% off MSRP and about 20% more than wholesale. That gives dealers some wiggle room to negotiate on price, but still keep their doors open. What is common for people on Amazon and Ebay (and other online sites, like gun broker) is to figure a way to buy at wholesale, then undercut MAPP because they don't need to make as much profit as a brick and mortar. Their overhead is MUCH lower. Then, when the consumer writes the OEM, They have to deal with the mess that the neckbeard caused by not doing things the "right" way. By the way, when you see an online store that makes you add to cart because their price is so low that they can't advertise it? Yeah, that's what is going on. They are selling for less than MAPP.
Consumer sales are a pain in the ass. I'm not really defending Yukon here, as I believe MFG's should stand behind their product, but it can be a bitter pill. Its akin to someone buying something at a garage sale, NIB, finding it doesn't work, then expecting the mfg to take care of it. Its new, but it was purchased on the second hand market. Should the MFG take care of it or not? Typically all consumer protection ends at the point of the first retail sale. Sales on Amazon and Ebay are more blurry along the 'retail' sale line.