This can be a difficult call, raising the age-old question:
How do you sell a car that you know will give the new owner serious trouble, even though the trouble is at the moment hidden?
That's the moral hazard.
Personally I'd try to do exactly what Robert has done - get your money back, and then plaster enough details around the internet so that anyone contemplating buying it will easily find the history if they do a google search.
Selling privately without disclosing the history would not be an option for me; in extremis, I'd most likely put the car into an auction.