I have sympathy with how you feel and how all the repairs required dent your confidence in the car. Have had a similar expereince myself with the following work done on my 03
MCS so far: -
1. new/reconditioned gearbox (always had fault since i drove oit ff forecourt was told "bring it back if it gets worse"! - was only after finding this site I realised how serious/common the fault was)
2. new bypass valve as down on power (dealer told me I had just become used to the acceleration!)
3. new boot handle as switch stopped working (had to go back 3 times as was intermittent and "no fault code reported sir"!)
4. New drivers seat base and runners as would get locked forward after letting people in the back.
In addition, despite my insisting the car needed new electric window motors four weeks ago I was told they just needed adjusting, two weeks later they fail completely....cue v annoyed mor7s on phone to service department to ask what they are playing at

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Upshot is it is in today for new motors, regulators, seals - the complete assembly basically on both sides and all under cherished warranty. While the car was being checked last week tech also spotted a rattle from exhaust and leaking sump gasket, so today it is having a new cat and sump gasket replaced

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To be fair to BMW/MINI they have never quibbled on a single job and I think the delarship is glad of the work at full labour rates etc etc. None of the bits they have replaced have given me a moments grief since, the battle is getting the things done in the first place at times!
mor7s