[L78M22Rag]

Maybe try a shotgun approach. Discuss and reach agreement with him as to how much value the original documentation adds to the value of the car. Whatever percentage that is (say 10% for simple math), then you offer to buy the documentation from him for $20k... (that mean's the car is worth $200k to you with documents - by using that ratio). If he thinks that's too cheap, then he has the right to buy the car from you for $180k (the other 90%). If he's not prepared to pay $180k for the car... then he has to sell the documentation for the $20k.... I'm not suggesting those are the values! Obviously you both have to buy into the process and live up to your respective end of the deal.