My E240 (1999, 50,000miles) blows dense white smoke (which smells like oil) from the exhaust when accelerating. This only happens when it's been run at high speed 70 - 80 mph for 40 minutes or so and you have just decelerated for a while. It then tends to run rough until its restarted, but with little more smoke. It's using oil; 6 litres in 4000 miles, but the coolant level is fine. It's back at the dealer now, who cant duplicate the problem, and claims to be mystified, although the computer shows that cylinder numer one has shut down several times. Is this a valve seal problem (or worse), and if so does anyone know of a similar problem occuring at this sort of mileage?