I switched to Mobil 1 at 75k on my M111, and developed a very small leak 1k after that. Luckily she was still under Starmark, and they replaced all my seals including head gasket (I'll buy CPO again for sure). That said, the leak was small, but you just never know. The stuff flows much better than dino oil. Just be prepared in case.

As for flushing, some other members have a great solution - a diesel oil, preferably either Delo 400 or Delvac 1, 5w40. The stuff is designed for HD OTR use, and it is like Mobil 1 on steroids as far as detergents. I would run it maybe 3k and change it. I ran Delvac 1 in my old Jetta TDI for the first time after 30k, and at 5k, I had 8% soot based on oil analysis. That's a LOT. That stuff will SCOUR your engine, safely

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former: 83 300D, 97 C230, 93 400E

current: 08 C300 Luxury , 92 500SL