It all depends of what sort of a leak we’re talking about here. If the tank is constantly leaking after it’s been filled up, there’s clearly some sort of hole somewhere in the tank or its plumbing from the filler neck to the tank proper. You could surmise that the level of fuel in the tank at which the leak stops, is also the level of the hole or crack. As the fuel drains further (as you drive the car) the fuel level is below that of the leak-point and the leak stops. Either way, this is a dangerous situation as even if there’s no liquid fuel leaking, there’s almost certainly fuel vapour escaping (which is more flammable than petrol itself).

While it’s rare for a tank to fail, much more common is having the plumbing which takes the fuel from the filler neck to the tank cause a leak. But if the leak stops soon after you’ve filled up, it could simply be that a small amount of fuel has sloshed out of the filler neck and into the car’s body near the neck, where it can drain away, thanks to gravity, towards the bottom of the car where you’re seeing it. Next time you fill up, be sure not to overfill the tank and remember to use the watering can on hand to slosh away any spilled or excess fuel.

The symptoms you’re experiencing all sound like they have something to do with the body computer(s) on the car. So it’s conceivable that a bad batch of computers on Mazda’s production line could affect more than one car. And if that’s the case, you’ve just been unlucky. That said, Mazda is not exactly a stranger to body computer glitches, and Mazda 3 built between 2015 and 2017 were, in fact, recalled to fix just such a problem that was affecting the operation of the windscreen wipers.

If you’re unhappy with Mazda’s approach, you can contact the ACCC to try to organise a resolution. But if the second car is only throwing up bogus tyre-pressure alerts and hasn’t started having other problems yet, then you should give Mazda the chance to put it right. The other problems may never develop, but if they do, I reckon you’d have a decent moral case for getting your money back. That said, Australia doesn’t have the `lemon laws’ that, say, the USA, has so getting a refund is not a simple matter.

The best approach is to buy a car from a well-respected brand, and stick with an Asian brand such as Toyota, Mazda, Hyundai or Kia rather than an European one. Models to consider would be a Toyota Corolla, Mazda3, Hyundai i30 or Kia Cerato.