"AS-IS" on a bill of sale is just about as done as you're going to get.
It was YOUR responsibility to have the vehicle inspected prior to purchasing. You chose not to. If you had hired your own mechanic and gotten the car inspected, you would have known exactly what was and was not wrong with the vehicle. You could have used that information to make an informed decision as to whether or not to purchase the vehicle, and whether or not the asking price was fair given the vehicle's condition.
Once you signed off on the bill of sale saying "AS-IS" and completed the purchase, you no longer had any recourse against the seller - because you accepted the vehicle "AS-IS", with all it's faults and issues.
You do not have a case. At. All. Feel free to spend your money on an attorney if you are still unsure, but it's almost a certainty that they will tell you the same thing - and charge you to do it.