Mike,
This might help you find the original owner or at least several after him... Call 800-772-1213. It is the Social Security Administrations letter forwarding service. Ask them for an office and phone# that's near you. Write a letter to the person that you know last owned the car befroe the guy you bought your car from. All you need is an address and a name. The SSA will look up in their records that persons address and if they are still alive will trace the addresses back to that person. If the person respondes with info you do the same thing again.
I got this info from a letter that came to my wife. She was very close to her cousin when they were kids. They have not seen each other for 35 years. Her cousin contacted the SSA and traced our addresses through the years and delivered her letter with a cover letter that says, "This person is looking to contact you." It goes on to also say that "We did not give them your address or any other information about you". "It is up to you to contact the person writing to you and you don't have to tell us what you decide to do."
My wifes cousin wrote to her in July and the letters came in late September.
Hope it helps!
Joe