I've been driving MB diesels for 30+ years and the new oil that was put in looked like the used oil that was drained out as soon as the engine was run and the oil checked on the dip stick.
I also have a Case Diesel tractor and the oil in that is always dark brown, even though it burns the same fuel. I can't explain why it is different. Another difference in the Case engine compared to MB engines is that the Case idles quiet like a gas engine and sounds like the hammers of hell under full load. Maybe its because the Case is a direct injection engine.
P E H