Personally I don't feel that there's a question being asked here
You've essentially backed an owner into a corner....who has untold money, mileage, labor, etc into his car and DOES NOT have the car up for sale,
...........and then suggesting "he's difficult to deal with."
My own junker is an excellent example. What is my time worth? What is the pain of arthritis worth? I didn't buy this car to flip, or even to sell, and I've got TONS of parts that "I might have needed" and uncounted hours of searching Craigslist, miles of travel, and just plain MONEY out the door that essentially will never be recoverable.
