I Know about this problem since one month. I have already asked my BMW dealer for the PP, and it will be installed in short. I have also had the run flat tyres removed as they are supposed to be partially responsable for the problem. I new about through de American Z8 Club, and appreciate the help.
Said this, it seems that if you dig into real figures, only 30 vehicules have confirm this problem in the States (1%), but some people are writting in different forums that 50% cars have it. No wonder nobody in Europe seems to bother much about this and prices have definetely not decreased. If you entre mobile.de you will find plenty of Z8 for sale (90 to 180K€) and, though many of them show a photo of the engine not even one show the performance packect transversal bar installed, though the price is not high in relation to the vehicule. BMW Madrid, the main house, has been enormously efficient with my PP, though nobody was familiar to the problem. At the same time, and, though it seems that a law firm has been contacted, no legal action has been started against BMW. All this make me think that may be the problem might have been exagerated a little by owrselves, the owners, within accepting its reasonable existence.