I have a Haynes manual for the A3 96 - 03, I believe there is no such thing for an s3. Anyway, in it, it says:

"The rear anti-roll bar runs along the length of the rear axle beam. It is an integral part of the axle assembly, and cannot be removed. If the anti-roll bar is damaged, which is unlikely, the complete axle assembly must be renewed"

Is this the case for the s3. I have noticed in other threads that people have uprated their rear ARB, have they had to go through this trouble?