My 84 and 85SD both start much easier in the winter on synthetic. I sent an oil
sample from my Cummins to Blackstone and was told that the oil was still in good shape and that the change interval on that engine could be extended to 15,000 mi.

Granted, a 24V Cummins is not a 617 and perhaps will send a sample from the Mercedes just for information purposes. The Cummins takes 3 gallons and the 617 ~2 gallons so the economics of paying for oil samples is different.

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85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.