Mine is also a "W123" model Mercedes; a 1982 240D.  My mechanic says 400,000 to 500,000 with "average" maintenance for the engine, longer for body (sans salt) and transmission.  With my maintenance (synthetic fluids), a potential million miles !

Mine is 4 cyclinder without a turbocharger, that adds a bit to longevity.

200,000 miles, 400,000 to go sounds great. That's equivalent to a round trip from Earth to the moon and back, plus gratuitous orbits! Just to put it into perspective. That's a lot of driving. If the drivetrain has another 400,000 miles left, it might actually last until the oil is gone. Just make sure your heat shield tiles are glued on good!

My Kia Rio has 50,000 miles on it and has a 10 year/100K warranty on the drivetrain. It's a Year 2001 model I bought at the 50,000 mile mark/5 year mark. 2 orbits, 2 to go for the warranty. Unfortunately, becuse Kia only recently emerged, nobody knows the long term reliability of Kias. New, they cost about $10,000 and mine was $5,000. With most of the depreciation out of the way it won't be long until I'm flying right-side-up financially. As gas prices go up, it might actually appreciate in value after a while - unlike SUVs. Meanwhile, SUV values will crash n' burn.