It's not just the drivetrain. Tesla is iterating toward "the Platonic ideal of the perfect car" i.e. one that requires NO maintenance at all. https://youtu.be/dLWrGc7E7TU?t=750

We definitely had some quality issues in the beginning for the early serial number cars, because we were just basically figuring out how to make the Model S. I think we’ve addressed almost all of those for current production cars. Not all, but the vast majority have been addressed in the cars that are produced today.

We're also getting better at diagnosing what's wrong. Because in some cases, particularly with respect to the drive unit, we would think that something's wrong with the drive unit but it's actually something wrong with another part of the car. We'd replace the drive unit and that wouldn't solve the problem because the drive unit was not the problem. In one particular case there was this vibration, and it was due to a cable detaching itself and touching the drive unit assembly and causing vibration to be transmitted to the body of the car. It was somewhat pernicious because if the cable moved a little bit so that it didn't provide a conductive path, the vibration would go away! So you'd replace the drive unit, you'd temporarily tuck the cable back, and you'd think the problem was solved. But then the cable would vibrate itself down and transmit the energy...

That cable thing takes us, like... it's nothing to fix it. It's literally a $3 cable tie to solve it. So there's a bunch of things like that which are just misdiagnosis problems, which we've obviously addressed.

There are a few items which will need - a fair number of drivetrains will need to be serviced. One in particular is related to the differential, and we need to shim the differential. It doesn't require a drive unit replacement, it just requires a technician to insert a shim. We're going to have to do that on a fair number of cars. But that's like a 50 cent shim. So it's really... I wouldn't assume that there's some vast number of drivetrains that need to be replaced, but there's several service bulletins that we'll be instituting -- many of which we have instituted -- to address the issue.

Every week I have a product excellence meeting (which is a cross-functional group, so we’ve got engineering, service and production) and we go over all the issues that customers are reporting with the car and develop action items that have to be addressed to get the car ultimately to the platonic ideal of the perfect car. That’s what we’re aiming for, because although I think we’ve got great service, the best service is no service. That's really what we want, is a car that never needs service. And I think we're getting there quite rapidly.

I think at this point we've got an excellent quality control team. We weren't there in the beginning but I'm confident we're there now. Our aspiration is an order of magnitude better quality than any other car, and we will keep at it unrelentingly until we get there.