Tell me all about these gearboxes...

[CliveH]

I've read the sticky and can see that these are problematic on these cars, especially if not serviced regularly. But, as usuaul, a few questions...

Is the weak point on these the gearbox or the torque converter?

Is this only difference between the S8 and A8 gearboxes the final gear ratio or is the S8 a stronger box?

I know that the similar RS6 (C5) box fails due to level of torque on that car, but what is the main reason for failure on the A8/S8?

When they do fail, I would assume that replacement is as cost effective as a rebuild, but do you replace with the same box/torque converter or is there a better solution?

Thanks in advance