Sold a road bike to a friend and then 3 months later complained the rear rim broke? No way.
Same friend tried it on with not paying me rent money, not paying his tv licence when I rented the flat cheap to him as a friend...well we're not friends and he didn't pay his last months rent but then again I did sell 2 sets of concert tickets delivered to the address after he moved.
Never ever do business with friends-lessons learnt.
I think you should buy the vehicle back if you have the money and repair the car and sell at full price.
If you were the buyer you could easily think the seller has ripped you off.
Paying 50:50 is a good gesture too as you sold him a car not road worthy even if you didn't know it would happen.