Pirsig mentions this in his first book, and I always related to that part, as I'm the kind of person that "feels" the pain when someone turns a screw more than it can go, etc. Searching on the pilot you mention and the date of the book, I wouldn't be surprised if he picked up the term from Jackie Stewart indeed.
I like you! Pirsig yes, Zen and the art of motorcycle maintenance - i got from Gemini it's Jackie Stewarts quote though.
Yeah, I see now my writing was confusing (it happens to me ...), as I meant to say Pirsig probably picked up the term from Stewarts.
In any case, great book. Gave it as a gift to my dad who was a mechanic when young and also rode a motorcycle (unlike Pirsig's' it as an Ariel though).