I would not call these ‘Grail’ pins, as they are not rare or special
But my collection will not be complete with out two Williams EM machines; Grand Prix and Space Odyssey
The two games that I first remember playing
Hard to top Fathom as a rare pin, Pete 
Rocket Ship would be near impossible to find (I know of one local to me).
A true "Holy Grail" would be like finding the fountain of youth - or the pinball equivalent - which could be a Fathom, or a Mermaid.
Grand Prix and Space Odyssey are EASY to locate and would not be much of a challenge. They are more "sentimental" machines for you ?
Sorry, I was refering to the game I nominated
Who am I to knock the games other people seek?
I was keen on your interpretation of a "Holy Grail" pinball. I know you would not be knocking other Holy Grail machines - and the offer is always open to play my finished Fathom
