Well now, that's pretty cool!

I'd suggest you keep in touch with the guy. Not too much to make him mad enough to ignore you, but enough to assure him you're both serious and able. Even if he doesn't want to sell today something will happen to motivate him. Could be tomorrow, could be three years, you never know, but you want to be the first person he thinks of when that moment comes. You may want to figure out where his head is, there's a reason he's been willing to leave the car in a shop for four years without going ballistic. He's gotta be motivated by something.