My daily driver is a w210 e320cdi and apart from the usual service items, its has been supremely reliable. I fitted the excellent egr electronic mod. a long time ago and the car has not put a foot wrong since. Your biggest problem nowadays will be finding a relatively rust free example. All in all the w210 is a fine car in my opinion. If your mate is looking at 2004/5 time frame this will be a w211 which is another story altogether!!