[The Newell]

Will,

low sulphur fuel # 1 has always been the choice of DD for the 2 strokes, DD now recommends no more than 20,000 miles for a two stroke between oil changes.

The TBN is the most important # in a oil sample and that changes with fuel and the type oil.

I have had to up the ash content to 1.31 in the oil on some of the equipment I owned over the years to get the TBN number right because of the type fuel I was using.
Never had a oil related engine failure on a 2 stroke 53, 71,92 or 149 series by following Stewart and Stevenson advice over the years.