Mine just got back and had to have one sheet replaced, but not due to the battery management boards, but one of the cells was at the top of the nominal range for voltage. I was getting 192 ideal range on a normal charge, it's just charging up now for the first time after having the sheet replaced - I don't expect much difference.
Also got new tires (had the performance tires, went for the 'regular' - they sure are quieter, but I've noticed the traction control kicking in slightly more often), had the driver side door tweaked (shuts a bit more nicely now, and the window goes all the way flush).
Compared to the 911, it sure seems a heckuva lot more reliable, and the cost of the service - accounting properly for the tires - was a bunch cheaper. I'm certainly happy.