Hi,
I have had a July 2004 ML270CDI auto Lux for nearly two and a half years and it is faultless, I have towed my last 3 caravans with it, the first was a single axle at 1400kg and the others were twin axles, one at 1700kg and this one at 1750kg.
Overall towing it does 20 - 22mpg and solo on a run near 30mpg, round town solo it is around 20mpg but at well over 2 tons and automatic it is as expected.
Max tow limit is 3500kgs and noseweight is 135kgs, I find mine very stable and the auto box is superb. I have driven the new model and it is a far nicer car but it is also a lot more money, there is a massive jump in prices from a late old to an early new model.
As mentioned before go for a face lift model, don't buy a manual if you can find one and make sure it has dealer history which will keep the 30 year Mobilife breakdown service.
Mine is for sale in a month or so and has a detatchable tow bar, 61000 miles, full dealer history and is very tidy.
spj.