To the OP. how would you feel buying a car and finding out the dealer hid $10,000 worth of damage? Say you bought a new car and after owning it six months found out your car had major repairs?
If you would be perfectly happy, and no complaints.. then go ahead and sell your car without disclosing.
The problem is they CAN come back and sue you. Just like you could sue the dealer who sold you a damaged car.
Just so you are ready to defend your deceit in court, you are OK.