When Clarkson, Hammond and May are crossing the Magkadikadi and arrive at Kubu Island, in the aerial shot the three cars are parked in a line. In the next shot, from ground level, Hammond's Opel is parked behind Clarkson's Lancia.
When the presenters initially introduce the faults of the cars they bought, May claims the handbrake of his Mercedes was broken 'which I can pull like this' (and nothing happens.) However, the Mercedes W123 actually has a foot-operated parking brake, with a pedal, and the upper lever lever May pulls to demonstrate is just the handbrake RELEASE. In other words: The parking brake was probably perfectly in order and May just hadn't found the somewhat smallish pedal yet.