Definitely plan to get ppi from local Benz mechanic that has been doing most of the maintenance on this vehicle. Before I spent the money on that I was just looking for a general yea or nay vote on used '06 e350s.We do have several members driving E class gasoline with over 300k miles.
Still those cars can get expensive to maintain and that is main reason why you can buy them extremely cheap.
Do not skimp on good PPI.
Regarding the balance shaft sprocket, all my2006 were potentially affected from what I understand, but there is no way to know when or if a specific engine will fall.