Thank you for using our forum. My name is ***** ***** I hope to assist you today.
I am sorry to learn of this situation.
Unfortunately based only on what you have posted, I do not believe that you have a basis to demand that the seller cancel or void the sale.
If I understand correctly, you purchased the vehicle and only after the purchase did you check with your mechanic who identified the problems with your state. The seller did not misrepresent anything to you, hide information about the vehicle, or otherwise try to mislead you.
Unfortunately this is a situation in which the seller has a right to enforce the sale as is.
Your best option here is to try to arrange a deal with the seller where they are willing to help you with reselling the vehicle, or perhaps enter into a cancellation agreement where they return at least part of your money, but again, based only on what you posted here, I do not see a basis to force the cancellation of the sale.
(I wouldn't recommend spending money to hire a lawyer to fight this - the amount of money at issue and the unlikelihood of finding a basis to overturn the sale make it unlikely that hiring counsel is going to be worth the investment).