Mercedes ML 270 CDI

What's the most sought-after item on a Mercedes M-Class? The wood-and-leather interior? The latest diesel engine? Or maybe it's just the badge on the bonnet that says you've made it.

Oddly enough, none of these is on the 'wanted' list of our long-term ML270 CDI. Instead, four tiny pieces of metal regularly attract attention in the car parks. They're the dust covers on the valves of the chunky off-roader's tyres. And, for some reason - much like the craze for Volkswagen badges, thanks to the Beastie Boys rock band in the Eighties - the Merc's metal protectors are the target of the thieves.

So far, around a dozen caps have been swiped while the M-Class has been parked. But it's not only the big Merc that's suffered from this. We've had more caps nicked from a new E-Class - while it was being tested during a week long stay with the magazine's road test team. When I called the local Mercedes dealer for replacements, this wasn't a surprise. "It happens all the time," the parts manager said. "People like the metal covers, and steal them to replace their own plastic ones." Ruddy cheek! Is there nothing they won't take these days?

I've been driving the Merc for a few months now and, with its class-leading boot space, it has proved a popular choice for a host of chores... it's been subjected to rent-a-van duties, transporting student belongings to university, while several trips across to the south of France and beyond by other staffers have been completed without a hitch.

It's on these longer hauls where the M-Class's turbodiesel engine shows its strength. Despite having only 163bhp on tap, there's plenty of torque to shift such a hefty vehicle. And the 2.7-litre unit is a first class motorway cruiser.

Around town, though, the five-speed automatic gearbox is constantly hunting for the correct gear, making smooth progress tricky and over-use of the brake pedal a tiring reality. It's much better to switch to the Touchshift manual function and do the cog-shifting yourself.

The engine, however, has a taste for oil which, on one occasion, caused an emergency call to the local dealer. A red light on the dash had warned that we should stop and seek immediate assistance, but it proved nothing more serious than an oil top-up. "It's a common problem to watch out for on these engines," commented the breakdown man in attendance. But it was a surprise nonetheless, after only a few thousand miles. A steering lock which refused to free itself on the key led to another, later callout. On both occasions, however, the response from the local dealer was impressively swift.

Meanwhile, fuel economy so far has been around 25mpg across a mix of driving conditions - that's good for the class. A petrol version returns less than 20mpg. Inside, the M-Class is generally comfortable, although the seats could do with better support, particularly as the 4x4 wallows its way round corners. And, in a vehicle which costs the better part of £30,000, you would expect reach as well as rake adjustment for the steering wheel.

But there's plenty of other kit in the cabin, with climate control, a CD player and curtain airbags all standard (and our test car also features an excellent satellite-navigation system from the options list). We expect the first service warning sign to light up any mile soon (it's due at around 15,000, we reckon), so watch out for further reports including service and running costs.