Many years ago I took delivery of a new Alfasud Sprint Veloce. Whilst demonstating to a friend how good the handling was I decided to brake hard and turn right down a side lane. To my horror, the brakes completely failed and clouds of white smoke billowed behind the car as I sailed on at full tilt. Fortunately it was a good spot for brake failure and nobody was at risk, but the consequences could have been far worse.
And which component was at fault that nearly killed us? A hydraulic bleed nipple in the engine bay that had not been tightened properly. All it needed was an extra 1/4 turn and it would have been fine. Instead the nipple released the fluid over the engine exhaust manifold creating instant thick white smoke.
A very apologetic team of mechanics arrived promptly and all was well.
The problem of being a new car owner is inevitably that you will become the tester of the car for all the subsequent owners. Any faults like small leaks are more likely to be found very soon after delivery. There are thousands of components in a car, and not all are capable of being tested thoroughly.