I did ask dealer if any warranty claims or service was on record for it, they said no.
I know diagnosing a situation from light years a way is dangerous.
My gut tells me the original owner knew he had an issue and unloaded the tractor to an unsuspecting buyer.
He likely called the dealer asking about the issue to cover up what he already knew. Perhaps this is a sign that he knew there were issues with the tractor that he was trying to hide, and called the dealer as an indication he was not aware of them.
I was not surprised at all that the original owner claims to have done the 50 hour service himself. Whether he did it or not. Who knows? Even if he had receipts for the parts and lubricants, no way to know if he used them on that tractor.
Unfortunate situation. In the end this might have had a better resolution if the original owner pursued it with Kubota himself. Except that he probably knew he did not have a case. Speculation of course.
What's the chances that a normally operating tractor, with only a hundred hours or so on it, after sold would fail in the first few minutes of operation after being delivered?
Not a betting man, but my bet would be those chances are about zero.
Afterthought: Is there any chance you could take him to court and force him to take the tractor back and give you the money back? Might be worth a try.