If ATF belonged in Engine lubricating oil, the oil manufacturer would put it there. My 300SD has 225,000 miles and recently when I had the valve cover off to adjust the valves, the head, camshaft or valve springs didn't have a bit of sludge on them. In fact the cam was so clean, it had a little rust spot between the lobes. I use Mobil I 15W50 and change the oil every 10,000 miles. The car is used mostly for long cross country trips up to 900 miles per day so this may account for some of the cleanliness. The enging still goes 10,000 between oil changes without adding any oil.
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