I know exactly how you feel.
But dont let it get to you and atleast they will do whatever to make things well.
Im on my 4th z4 and none have been plain sailing, and anyoune in the right mind would think dont get another, but bmw have always fixed them possibly not the first time, but you can work the system. Mine is picked up from work, and dropped back, or a hire one dropped off while its away.
My first one was a 03 2.5 SE got it in 05. Rattles in the roof, leak in the doors seals, sat nav display blowing, rear brak light cracking, It went in countless times. One of the worst was when they were sorting out the rattles, all fine, had a hard top on, when I took it off few months later, seen that they had damaged some of the rear trim and all joints had silicone which had collected dust, it look awful. They sorted it.
Second 06 2.5 si sport, wheel corrosion, engine missfire 3x to sort, fog and side lights misting up all sorted
3rd 08 si sport. wheel corrosion all 4 replaced, wheel corrosion (yes had rears replaced again) new soft top due to rubbing when the hard top was on, corrosion on petrol cap and boot. fogs misting. took a few goes to get these fixed.
4th 10 3.0. both front lights misting, and one rear actually has water in it not just fogging need to get this sorted.
So I must simply be mad, but still keeps my local dealer in a job by claiming on all the rework.
Seriously I have no regrets on any of them. Its not good that the issues arrise but they do get sorted, and for me its been seamless other than a phone call to the dealer, last time when it went into its last service/ pre mot they were picked up and ordered all on wty. it did take 3 months to sort (so out of the origional wty but no cost) and the car was in for 2 weeks, but had a hire car at no extra cost.