My wife bought her z4 convertible a few months ago. The first problem was that the passenger window would not close completely after the roof was raised. This became worse and a gritty tearing noise began. We took it in to our local garage and ended up paying over 300.00 for new parts. It now works beautifully. The other big problem was that the manifold was cracked (2.0ltr) engine. I learned about it from the forum that this engine was often affected by this fault. We had it welded successfully for around 280.00. I'm happy to say we both love driving the car which now seems OK.