The original Vapor Records Boxcar.
Note I do not mean the quite readily available 6-29218. It looks just like that car, but it's basically almost impossible to tell the difference from the deco on the car itself.
I don't have the details committed perfectly to memory (but I know it's in the back of one of the McComas price guides from years ago ), but I believe you need to open one of the boxcar doors and peer inside to see a stamping on the frame inside the car, and also have the shipping carton, which may be the only thing with the different catalog number called out on it (not sure if this car has a label on the end of the regular box or not - again, details not quite committed to memory 
)
I'm pretty sure I've never seen one for sale (and I made sure to look at the Neil Young auction from Julien's a few years ago to check!) . Every time I look at a table, everyone asks "what are you looking for ?" And when I explain, nine times out of ten they will not know what the heck I am talking about ant they will only think there is one of the cars that looks like that.
I'm pretty sure I will never end up with one, even if one did come up for sale, I would probably not be willing to part with the price it would most likey command. But the title of the thread is "Holy Grail"! 
.
-Dave
