FYI
http://www.z8-club.de/cms/en/node/316
I found this out via the Club, which sent me this free of charge, another benefit of being a Member. My car is in winter hibernation which means its up on a lift and I will drive it once every few weeks but not too often. I plan on installing this in the Spring when the weather is a bit more mild.
The reinforcement-bracket for the rear bumper (bottom part) of the BMW Z8 is solely developed by the BMW Z8 Club e.V., it is made of brushed stainless steel and manufactured in laser-cut-technology, it is exclusively available from the Club-owned Z-Acht GmbH.
The often occurring bulging of the bottom part of the rear bumper will be completely prevented with the installation of the reinforcement-bracket. Without the reinforcement-bracket this bulging can lead to massive noise development in the tail area of the vehicle due to air circulation and resonance and eventually leads to tears in the lower part of the rear bumper next to the screws.
Full info from the Club is also posted here - http://www.bmwz8.us/chat_frame.htm