The first piece of advice here is to not drive the car at all until this problem is fixed. A car with faulty brakes is one of the most dangerous situations you can find yourself in, and it’s just not safe to even attempt to move it, even to relocate it on the driveway. The problem could get a lot worse very quickly, leaving you with no brakes at all. And even if it doesn’t get any worse, your limited braking capacity could make an emergency situation much, much worse.

The noise is probably not brake-line pressure escaping, since you don’t have falling brake fluid levels. At which point, my suspicion becomes that the brake master cylinder is at fault. This is a device that uses vacuum from the engine to assist you to push the brake pedal. If the diaphragm inside the booster fails, you will might hear the vacuum escaping, with a hissing noise. Even if the booster is intact internally, a simple hose that connects the booster to the engine could have split and caused the leak. Until it’s fixed, though, you won’t have full braking power and that’s, obviously, very dangerous.

That’s getting up there for any car, even though modern engines are capable of much greater distances than their older relatives. But that sort of mileage does raise some questions.

Those start with how complete is the service history. If there are any gaps, this would be a car to avoid, as any vehicle with that sort of distance covered will only be as good as its servicing and maintenance allow. The other question is what sort of life the car has led. Three hundred thousand kilometres sounds like a lot, but if you break it down to kilometres per year, it works out at less than 18,000km per annum, which is well within the bounds of normality.

However, the bottom line is this with all high-mileage vehicles: You might get lucky and get another 150,000 trouble-free kilometres out of the thing, or it might go bang tomorrow. That’s the punt you take and that’s why high-milers are cheap to buy. Which is another way of saying that even with a full service record, a RAV4 with that sort of mileage would still need to be cheap.

Without a doubt, the best thing to do now is the have the car electronically scanned. That’s because there are literally hundreds of things that could cause this sort of problem, ranging from (but hardly limited to) a sick fuel pump, a blocked fuel filter, worn injectors, a fuel leak, poor ignition, a low-voltage battery, dirty air-filter, blocked or damaged exhaust, a stray electrical problem and much, much more. Even something simple like a fuel rail that is not holding pressure when the engine is switched off, can lead to symptoms very much like yours.

Hopefully, the on-board computer has logged these random starting problems and will be able to tell a mechanic what’s wrong. Otherwise you’ll simply continue replacing parts that weren’t the problem in the first place. And that costs time and lots of money.