The diesel motor is not a problem but the rest of the systems, including the AC, water pump, appliances, furnace, TV's, slide motors, leveling jacks, furniture, etc are all 16 years old. Also, unless they have been changed, all hoses belts, etc, on the engine and transmission are also 16 years old. The radiator, which can be very expensive problem, especially if used in a salt laden environment, is also 16 years old
Does the owner have complete service records so that you can see if it was maintained according to manufacturer recommendations? If he tells you that he did all of the maintenance himself, which I do, then you have to take him at his word, which is tough to do with a total stranger that is trying to sell you something.