I think NADA is the best. Edmunds is next. Kelly is dead last in determining old diesels. Those are the three books I am familiar with.

Don't even look at Kelly, you'll faint if you owned a diesel.

In fact, older cars are sold by exclusivity. Cars with books and records since new, original paint jobs with very few blemishes will sell for many MANY times the amount the books claim they are worth.

Use your gut feeling. What is it worth to you? If it IS a "no-stories one-owner automobile", buy it (after a little negotiation, first). They are almost impossible to come by. See if any parts were replaced recently, and what may need work. Have it checked by an honest mechanic.

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1987 300SDL (324000)

1986 Porsche 951 (944 Turbo) (166000)

1978 Porsche 924 (99000)

1996 Nissan Pathfinder R50 (201000)