I know what you're going through, my 2nd GN was bought via a classic car retailer and had a similar issue but with rod knock that you only noticed on dry start up. Got nothing due to as is BS.
Take it from someone who's had others F up their stuff and get away with it because the drama isn't worth it, you eventually need to stop being a doormat. Even if you don't recoupe any $, don't let them think they can get away with this and not have any smoke come their way, add stress to their lives too.
Winning isn't just about your money, you can hurt THEIR future $ by being a loud voice to warn others from buying from them. This is how you'll crush them in the long run, the better you do at online posts, create a website even that documents the whole ordeal, BBB filing, actual court case that shows you won etc, hell even do physical marketing, you can dry up the well and then they'll have to sell or close shop.
Proof and a disciplined long game will take them out, keep track of everything and run things by your lawyer if you wanna start up the marketing of "Cons and Cars" campaign.
Good luck