Some cars are just trouble. It doesn’t matter what you do to them, they just keep creating new faults or have problems with reoccurring faults. This could well be one of those cars, but on the other hand it might have just suffered a failure that has now been repaired, you just do not ever know.
The fact that you was able to hand the car back to them and not even take a second look when you did says to me that you really didn’t have much of a connection with that particular car.
To this day I really could not tell you why I brought a Z4. I will get shot down in flames for saying this, but I actually think there are far better cars out there which come under the the same category as the Z4, and I had the option of buying several, but there was just something about mine that caught my eye. From the test drive onwards I just connected with it. There were elements of the test drive I didn’t like, such as the notch from the gearbox, the rattles, the tramline from the runflats, the unexciting engine noise, but I was able to see through that and felt like the car had real soul.
I find myself always looking at my Z4 wondering what it is that I find so appealing, and to this day I still could not tell you, but what I do know is there is something about this particular car.
If you haven’t found that with yours (or what was yours) then maybe keep looking. Just my thoughts for what it is worth.