I have met Mark and he is a very fair and easy going person so here is a suggestion...
Could you possibly agree to get copies of the doucmentation with the original owner keeping the original paperwork with the first option to buy the car when you decide to sell it?
That way you could display the paperwork with the car....but keep him in line to buy it.
...I would think that he feels if he ( the original owner ) releases the paperwork , he will never be able to be the first in line to buy the car back.
...good luck on changing his attitude
