Lubricants have changed since the Kohler K and M Series engines were designed.
But what has not changed in the slightest is Kohler's recommendation that a straight grade 30W detergent oil be used in those engines.
Kohler states that multi-grade 10W30 is acceptable when the ambient temperature falls below the freezing point of water BUT...you must keep a diligent eye on the level of oil in the crankcase because those engines will consume multi-grade oils faster than straight grades. None of the "improvements" to oil technology has overcome that issue. Greater oil consumption leads to faster build-up of carbon deposits in the combustion chamber. Increased oil consumption also puts the engine at greater risk of failure since most failures are caused by a lack of available oil.
And if synthetic oil was truly the panacea that so many people think it is, then why is it that Kohler did not recommend using it? After all, synthetic oil was around before the advent of these engines.
It always amazes me that SOME people who have no background in lubrication engineering feel compelled to give advice about choice of oil that goes against all of the research done by the very people who built these engines. If they are half as smart as they think they are, then a career with Kohler's engine division awaits.