My friends E300D seems to have run on 0w40 for a large chunk of its first 140k miles.

0w40 is just fine for diesels, its soot suspension where it lacks. Don't drag the changes out to 15k miles and you will be fine. Well half that on the old ones.

Having said that the MB dealer that I use, does use Delvac 1 or whatever they are calling it now in the diesels that come in. Everything else gets 0w40.

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2016 Corvette Stingray 2LT
1969 280SE
2023 Ram 1500
2007 Tiara 3200