I am an advocate of synthetic oils and have been since the mid 70's when it first became available. I have not used anything else on my cars since, especially Diesels. I lived in Alaska then and Mobil 1 was the only reason the car started when it was not plugged in during the Winter.
I have just taken the head off my 1986 190E 2.3-16 to repair a burned exhaust valve. The job is taking forever due to problems with parts availability, but that is another story. I was awed by the condition of the engine when I took it apart. There was a little more discolored oil on the engine internals than I expected, but none of it would not just wipe off. The cylinder bores were like new, original cross hatching from the honing still intact, and no metal ridge at the top of the piston stroke. The piston tops are a little discolored (black) but those are likely deposits from the last ride before the engine was torn down, as it was running really poorly. I have enclosed a photo, and I hope it comes through.
By the way, the car has 206,000 miles on it and this is the first time the head or any other major engine component has been removed. I look at the results as evidence that synthetic oils are in fact better at protecting engine internals from damage in high performance cars or harsh operating conditions (Diesels). The way I look at it, the extra cost is not wasted. Good Luck, Jim
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)