My story isn't as impressive, shorter time frame too.
Back in 84, my dad bought my mom an 84, so they could go cruising together. He had a 71, which he later sold to fund the move to Florida. Eventually it got kind of run down, so we started working on it together. At some point he got frustrated enough with it that he began calling it "your stupid car". I of course had no problem with that. He didn't either, until I started calling it "my Vette", which apparently made him decide that is wasn't. Ever since then whose car it is depends on what it does when certain people drive it. Generally speaking, if I'm driving it and it breaks, it's his car. If he's driving it and something breaks, it's my car. If it runs funny, it's my car. If anybody is driving it and something small breaks (like a AC switch) it is his car and I broke it, even if he was driving it when it broke. Whenever money is put into it, it is his car (whoever pays). When insurance comes due, it's my car. When everything works perfectly and a shooting star passes precisely overhead, it is "our" car.
Currently, my dad has bought a few cars and seems to have no interest in ownership of the Vette. Especially since he got the XLR, when the transmission went out he even said it was my car. How long this will last, I haven't the foggiest. I'm hoping to prolong it for as long as I can after I put the new transmission by carefully referring to it as "the Vette".
So I suppose that you could call it a family heirloom. This may not be accurate from week to week, but that's the best summary I've got.