That is about what I expected from Kubota. Kubota could care less what Cat or anyone else has in THEIR warranty. You bought a Kubota and they apparently don't make house calls in the first 6 months. I don't think the thought of repossessing the machine is going to be a big motivator for Kubota to do anything. They will likely have some third party repossess the machine and whatever that costs will be added to the default amount on the machine. I doubt that really matters to them, if someone repossesses the machine with a medium lift helicopter, so be it. If your default amount is 50K on the machine, it will be come 65K after the machine is flown out. No skin off them. I very much doubt a letter from a lawyer will move Kubota either. Are you going to sue Kubota for breach of contract? The short version of the contract is they agree to sell the machine. You have a warranty period and it is your responsibility to provide the machine to them (the dealer) for any work. The selling dealer isn't obligated to go to you to fix it, even though that is a service typically offered in the industry, they are not under obligation to provide that service, even when paid to travel. The poor reviews of the dealer were justified, you took the time to research that, but didn't heed what you learned.
My suggestion would be to have the machine fixed. Forget you have a warranty, because in your case, you really don't. Your breaking your own heart trying to extract help from the dealer or the OEM. Have it repaired third party and get the machine back to work. When you have the ability, trade it on something else. Why wont you share what dealer this is?