Trying to select a winter oil for my 1978 300D (non turbo). I have read the various oil threads and have come away with much knowledge, but I have one specific question and would like a specific answer.

The specs on the back of the Rotella state it covers various API "C" standards as well as some manufacturers specs including "MB approval 228.31".

The back of the Mobil 1 Turbo Truck Diesel states only it "meets or exceeds light duty including Powerstroke, Duramax and Cummins". It also says "Meets or exceeds heavy duty including Mack, Detroit Diesel, Caterpilla and Navistar". It also states "Meets API SM, SL and SJ".

So the Rotella covers "C" stuff and mentions a Benz spec. The Mobil covers "S" stuff.

Which do I want. My car currently has Shell Rotella 15-40 in it. NO oil leaks other than the PCV elbow joint on top of the valve cover.

Thanks in advance, also apologies in advance if it becomes an oil Jihad