I once had a similar case that involved fraud of an automobile. An attorney was hired. I won the case and a judgement. I never collected. The Sheriff told me at the property that he could only confiscate things on the outside of the house to use as a 'payment'. It was a hovel. I'm telling you this as a 'been there done that' story.
As the others have said, 'As Is' is a binding contract. As I have shared above, even a win isn't a win necessarily. I'm terribly sorry for your having been mislead, for your disappointment, and for the money that you believe has been wasted.
However, if the tractor is operational then it didn't burn up from loss of fluid. That is a good thing. There are really smart and patient folks on here willing to help. That is a really good thing. You may have to get dirty. You may have to do a repair/refurb/modification/fabrication that you weren't expecting but I wouldn't count your money down the toilet, your emotional frustration notwithstanding.
You can document and try to appeal to the seller, but in the end unless he is just a stand-up guy and wants to clear his conscious you have bought a tractor that needs a serious leak fixed. Again, I'm sorry, and feeling as wronged as you many years ago I went to the mat in a serious way. It only led to prolonging my frustration.
Fix your new tractor and when you finally wipe your hands clean, literally and figuratively, you will feel greatly relieved I believe.
Ed Fisher
Dallas