Managed to fit my S system last weekend. All old brackets and system came off OK although I did soak all bolts with penetrating oil an hour or so beforehand.
Used 1cm nuts to lower rear mounting brackets and everything lined up fine. Trick seems to be to do everything up finger tight, and then tighten from front, centreing it as you go. Only snag in the process was that the 6 M8 nuts for the bolt on brackets were missing from my kit. Easily fixed.
Really pleased with the quality, service and appearance of the system.
Particularly glad to get rid of the beer can appearance at the rear.
Only disapointment is that the sytem is as quiet as the original! My wife did not realise it had been changed. It is a much nicer noise with a burble at idle and the overrun popping has lost its tinny sound, but under load no noticeable difference to the BMW one that came off, either internally or externally.
It does seem from this thread that they vary a bit.
Has anyone tried it without the central silencer at the front of the system.
cheers