The story you mention is mostly accurate. It was researched pretty heavily by a couple of Tucker Club founders back in 1974 which was just a couple years after it happened. Over the years the story has been shortened a bit. The main part of what happened is left out of most of what we hear now. The person that had the Tucker in his possession decided to store it at a rental home he had. The renters complained many times and asked him to move it. At that point, according to the story, he became ill for a period of several months and did nothing to get the car moved. Finally, months after being asked to remove it, he went to the rental house and it was gone. The renter said they knew nothing about it.
Of course we'll never know exactly what happen unless we find the renter but I think we can pretty safely assume the renter had it removed either by calling a scrap dealer or calling the City and having them remove it. If the renter had it removed, would they really admit it and risk angering their landlord or would it just have been easier to deny knowing anything about it?
As to could someone sell it now? I'm sure any statute of limitations has long run out. Since the person that had it in their possession found the car and had no title to it he would have a tough claim. On top of that he passed away in the mid 70s so his family would have to prove some claim. Since no one else can prove that person ever had the car and there is no documentation I think anyone finding the car now is pretty safe.
I do think we have to accept the car is gone and let it go. If we leave open a large possibility that it is floating around yet, sooner or later, we'll have to deal with someone trying to pass off a car or parts as real.
