This retrofit has been succesfully implemented and tested on mine A4 B9, and it’s still active.

In order to retrofit the S-Line diffuser, you must already have the S-Line rear bumper. You can easily recognise it from the small honeycomb grill, watch the photo below. 

Once you’ve ordered the part listed above, you need to unmount the rear bumper of course.

Watch the photo below to note the mounting points of the exaust brackets and diffuser. 

The single \ double exaust pipe must be cut out about 10cm.