Valvoline VR1 Racing SAE 20W-50 Motor Oil

I had a good customer of mine come by today with a zero turn with a Kawasaki engine. He brought his own oil and filter asking for an oil change. He bought these at a dealer (they sold him the wrong filter, but, that’s another story…) and two dealers both told him the same thing - even though the owner’s and service manuals recommend 10w40, Kawasaki is recommending 20w50…