A few months ago, I noticed a small cloud of smoke drifting from underneath the car - thought no more about it, as it didn't recur.

Yesterday, my pride and joy (complete with family and self) were Green Flagged home 200 miles, as the transfer box had destroyed itself....

Gradually, as we headed towards London on the M40, the knocking noise was getting louder and more worrying, so we decided to get some advice. (One of those moments when you're grateful for smartphones...)

I owe a big thank you to Mark at MDM Technik in Marlow... wife and twin 5 yr olds were offered warmth, comfy sofa, and juice and coffee while Mark and I went out to listen to the noises from under the car and then put it on the lift. This on a freezing cold Saturday afternoon, when the Big Boys have pretty much shut up shop... and a very reasonable bill for his time, I thought.

Anyway, it would appear that the smoke would have been the oil exiting from the transfer box, and evaporating as it hit the exhaust that runs under it. Since when, I guess, the box has been running without lubrication. It finally did what you'd expect it to do, and disintegrated. Although the car was still driveable (but making nasty noises) the mechanism or the heat had cracked the transfer box casing.

(For those who don't know, this is the box that takes the drive to the rear wheels - it's between the prop shaft and the gearbox.)

Cost of new parts around £1400, plus around 3hrs labour, it would seem.

Softening the blow is the Momentum warranty we stumped up for when we bought the car (not from a franchised dealer) last year. But the claim limit is £1000... didn't spot THAT in the small print at the time!

Does anyone have any idea if this is a common failure? Any thoughts as to what has caused it? My own guess is that it's the result of a previous owner replacing tyres haphazardly, rather than as a set of four. (I was warned of the dire consequences of doing that when we had a Touareg - same applies to quattros and 4motions, I believe.)

But I'd like to know if it could have simply been a manufacturing fault, rather than the box being stressed by unequally-circumferenced tyres.

I'm guessing that, on top of having to pay a few hundred towards the repair, I really ought to buy a set of tyres immediately - but is this issue of relative wear really that big a deal? Or just VAG covering themselves? (A sort of automotive equivalent of Dry Clean Only labels...)

I'd be grateful for your thoughts, folks. Thank you.