You raise a good point about the repetition of the metaphor in question to the disciples might indicate that it was NOT meant as a parable.
But that isn't necessarily true because Jesus often spoke to the disciples in parables too.
I've looked on Amazon and Whole Foods but I have been unable to locate any leaven of the Pharisees and of the Sadducees. I was just curious.
Might the blood and flesh referred to also be metaphorical? As in the teachings and Words of Jesus?