It's preferable the fuel state stays as it is. How do you know it's not the amount of fuel otherwise?

Presumably the engine was only idling during their decent if the only thing that slowed their car was 'miraculously' grinding the car against the mountainside.

So, using previous records, they should estimate fuel usage during the decent. Then they should walk to the nearest fuel station, purchase fuel, and walk back. During that time, they can calculate the amount of fuel that will evaporate while they have the gas cap off and the amount of fuel that will stick to the walls of the piping between the gas cap and the fuel tank. This way when they return to the car, they can put in almost exactly the amount of fuel that was consumed during their harrowing stop.

This presumes the fuel station has the same mixture as they have in their tank. Otherwise all bets are off and they should simply give up.

OBVIOUSLY, you could have solved the problem with motor braking. The driver is not going to accept fault until there is conclusive evidence of the their wrongdoing, but you can't let the team know you are going to repeat the test again but with a different driver because then they will invent objections to pushing the car up the hill.

Turn the car around 180 degrees facing up. Coast down the hill in reverse and control your descent with the throttle.

"Magic", "More magic."

The brakes failed, but nothing claimed that they will fail again. So, it's suggested to run the test again.

Of course but they could run the engine instead of pushing the car.

Reminds me of the Family Guy episode (I think) when Peter and Lous are both running for Mayor (or whatever) and were going to a debate. Peter had his brakes cut and when he arrives says "Sorry I'm late! Breaks failed" to which the response was "Shouldn't you have gotten here sooner?"

That was a Simpsons episode. S9E22 Trash of the Titans.

Ah thanks, damn. Mixed up my adult animation. I swear I can picture the entire scene as Family Guy characters in my head though.

You are assuming it goes backwards or uphill. Better test that with a unit test.