AFAIK, the daughter card in the MCU1 contains the solid state memory (eMMC) that fails in these units due to too many write cycles in the past from the Tesla firmware. The repair reportedly costs about $500 outside warranty. The SC took three days to install the card and get the MCU working again, including needing help from Tesla in Fremont. I've also read that the new daughter card has more memory than the original, and I'll speculate that this could be why the SC had trouble integrating the card into the MCU. The shop receipt says they had to do some "firmware update", buy the overall vehicle firmware level didn't change.