You have the right to terminate the transaction and return the car with a full refund of your money or to have the seller pay for the repair...your choice. Even though it's a used car and the seller may have made no warranty, you still have recourse. A seller is obligated to disclose anything the seller knows or should have known that a reasonable buyer would consider material in making the decision whether or not to buy the car. This gas leak is clearly something the seller knew or should have known about and it clearly qualifies as a material item that a reasonable buyer would consider in making their decision. Even if there was no warranty, you can tell the seller in buying the car without a warranty you were relying upon his duty to disclose anything material he knew. If he does not agree to take the car back and refund your money or pay for the repair, you want to raise the stakes on your seller. In that case, you should send the seller a certified, return receipt requested letter detailing the history and misrepresentation and lack of disclosure and demand he take the car and refund your money (or pay for the repair, your choice) in full within a short specified period of time. Inform your seller that if your demand is not timely complied with, you will have no choice but to file a suit against him for your damages. BUT, be sure to specifically mention that if forced to file suit, you will be filing this claim not only as a breach of contract case, but also as fraud and deceptive trade practice causes of action, which will entitle you not only to your damages, but also an additional amount equal to multiple times your actual damages as punitive damages. That should provide plenty of incentive to comply with your demands; but, if it does not, file your suit. Even if you have to file the suit, that's likely all you will need do. In my experience, the seller will settle this without a hearing rather than risk punitive damages and the fraud and/or deceptive trade practice judgments being on the record.
Thank you so much for allowing me to help you with your questions. I have done my best to provide information which fully addresses your question. If you have any follow up questions, please ask! If I have fully answered your question(s) to your satisfaction, I would appreciate you rating my service as OK, Good or Excellent (hopefully Good or Excellent). Otherwise, I receive no credit for assisting you today. I thank you in advance for taking the time to provide me a positive rating!