I would send them a legal letter with a bill for the replacement of the gearbox parts. If they don't pay up then issue them with a writ and take it to court.

Write down everything they said and you said while it is fresh in your mind.

If you start from the proposition that YOU DROVE THE CAR THERE, therefore it was not broken before they drove it AND YOU DIDNT DRIVE IT AFTER THAT. Then logically there is no other explanation but that they thrashed it and broke it.

OH ANd before I forgget, make sure you keep the broken gearset and film it coming out of the car and showing the damage. That way you can show that as evidence in court.

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