Where should the vehicle be parked when checking the oil level of the gearbox?

The correct choice is to park the vehicle on a flat road when checking the oil level of the gearbox. This is important because a level surface ensures accurate readings of the oil level. If the vehicle is parked on a slope or incline, it can lead to an incorrect reading due to the gravitational pull causing the oil to shift towards one side of the gearbox. This misrepresentation of the oil level can lead to either an overfilled or underfilled condition, both of which can cause damage or failure in the gearbox operation.

Parking in a garage may provide some shelter but does not guarantee a level surface, which is critical for ensuring an accurate measurement. Therefore, for the sake of maintenance and operational safety, a flat road is the ideal and most reliable choice when performing such checks.