"Without fully and finally letting go one’s self-with-form, there can be no transmission — even if one has received innumerable transmission certificates from various lineages. The basis and source of transmission in Zen is the awakening to one’s selfless self. And this emerges precisely from the dropping away of self, once and for all. Remember the character I wrote on the board? That’s it. No one transmits anything to anyone; in other words, shin or kokoro transmits kokoro to kokoro by way of kokoro. That’s all."
The Source of What: Who Transmits What? (PDF) by Jeff Shore is a wonderful summary of the issue that combines both the Zen and the scholarly view.