I would definetly not drop the oil pan myself. By all means go to the general manager and tell him or her what happened. See what you can work out with them. If the GM wont make good then you should go to small claims court. Tell the judge exactly what you have told us that the sales person told there was absolutely nothing wrong with that tractor. If you have another shop give an estimate of what is wrong with it take that to the judge. If you take the oil pan off the sales person can make the statement it was working fine when you bought it and he has no idea what damage you caused while the oil pan was off. Having a qualified service person take the pan off for troubleshooting purposes is much different than doing it yourself. I would not do anything to the tractor your self until after you have this issue settled.
Once again I find myself in agreement with Gemini.
GOOD ADVICE.
You were played for a sucker and need to take some proactive steps to even the score a bit. If they said there is nothing wrong with the tractor they are tacitly claiming knowledge, and giving an expert opinion of persons experienced in the business and should stand behind their representation. On the other hand if they said they know of nothing wrong with the tractor they are claiming ignorance and that is different. Of course if they are experienced professionals the claim of ignorance may be a bit shaky.
The sleaze factor seems to be very high on the part of the seller and with any degree of fairness on the part of a judge you should get a reasonable degree of satisfaction. You may find the sleazeballs are more inclined to try to "cost share" with you rather than come under a bright light of scrutiny in court.
Beware, of rushing to judgment and accepting any "deals" to settle out of court. Settling out of court is OK if and only if you get what is fairly coming to you. It is likely they are well practiced in this game and will offer to share a cost so inflated by them that your half may still give them a profit, taking you for a "tractor ride" a second time while pretending to be doing you a favor.
You need to be flexible. Remember if a deal seems to good to be true it just may be too good to be true. So along these lines and presenting flexible alternatives you should consider offering to settle for their refunding 100% of the purchase price and your returning the tractor in lieu of repairing the ractor such that it is as good as their expert claims made prior to money changing hands. Let them choose from among: 1. take tractor back and refund 100%, 2. fix the tractor to the condition represented prior to sale, or going to court and taking their chances.
I am NOT A LAWYER, did not stay in a Holiday Inn recently, and don't practice arbitration professionally BUT I am not a stranger to certain legal proceedings which I have observed. A word of advice: Don't be too one sided in court. Ask for a fair result that is fair to all parties, given the circumstances.
Good luck, man. I hope you get a reasonable resolution of your situation.
Pat