Agree with
@Kajtek1 on that drivetrain. It's very reliable and very solid.
The time will come when you will need to replace the control arms, both upper and lower. The car is getting to about that age where that will be due if it hasn't been done already. This is true of all cars, BTW, and you will want to stick with OEM parts, because those are the good parts that will actually last you those 10 years. The thing is, being a 4Matic, the good control arms, to my knowledge, only come in Genuine-MB brand, which means the dealer. I'm not aware the Lemfoerder or TRW, the two big OEM's for MB suspension parts, sell those under their own brand (for 2WD, they do--go figure). So, look at US $1,200 for both sides when that comes due.
SBC is another thing. That pump is about $1,200 for a MB-reman'd pump--the only way I would go--so that's a good expense.
With all of that said, if you do get your car into "good repair" and keep it that way, which by my personal definition means you'd trust it on a trip from Vancouver, BC to Halifax, then that car will last you
at least 10 years without needing anything major and probably considerably longer with virtually no fuss. Mercedes-Benzes with that drivetrain, kept up properly, generally are darn near as reliable as Hondas, and since we own several Hondas as well, I am qualified to make that statement.
So, count on a few thousand after purchase to get it into "good repair", remembering my definition. In return, you will get a car that will take you around the globe and then simply ask, "wassup next, boss?"