Arco Petroleum made a Graphite impregnated oil back in the 1980's, graphite is a great dry lubricant and Arco and I both thought it made a great motor oil additive, so I bought a case and ran it in my #72 for a couple years. When I rebuilt the engine it took me 2-3 hours to get all the black graphite off the bottom of the pan. That oil was only on the market a year or two.
I've been using Rotella 15W-40 oil in ALL my tractors, BIG and little, the Kawasaki engine manual for my Cub Cadet TANK recommends Rotella by name too, I use T-4 in the Tank and the 982, & 70, and Full synthetic T6 in the Hot-Rod K321 in the #72.
It's been quite a few years since I called Shell Oil's ANSWER MAN, they used to put the 1-800 phone numbers on the jugs & cans, I've asked and they have answered that the amount of ZDDP in Rotella varies by viscosity and grade, but most grades have 1200 to 1400 PPM, parts per million. More than plenty enough to protect the camshaft lobes and cam followers in any Kohler. Now if you had a BIG Block Chevy or a Hemi you wanted to Rev to 8000-9000 rpm a L-O-T, you might want to add a bit of supplemental ZDDP.