Not to add fuel to the fire, but if I'm experiencing blow by wouldn't soot loading be a concern and cause the oil to become "contaminated", for lack of a better word, before it's time?

I know that I can extend the linterval for syn oil, but without testing the oil every few thousand miles the only indicator that I have to go on is the color of the oil. Color = nasty.

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1974 240D "Boldie" 170K.- New timing chain/freshly rebuilt IP/replaced valve seals/injectors/upgraded stereo/new Bilsteins with Yokohamas/fresh paint and rocker panels plus lots of welds.