In the owners manual, Kawasaki only recommends a API SL oil. The newest ratings are all backwards compatible. I asked Kawasaki why they say API SL, and they say because of the zinc and phosphorous levels are reduced in the newer rated oils. Thats the 20 and 30 weights only. And besides there are other anti wear additives too. I asked the minimum amount they like to see and they said, 1000 ppm. Mobil 1 0w40 will meet that. This is my thinking and it as well be the OP thinking, why pay for the OEM's when you can buy Mobil 1 at the same price? And besides you can find Mobil 1 or other full synthetics easier on sale. Using a 5w30 or 10w30 synthetic is not bad for the engine, but for a piece of mind, you can use Mobil 1 0w40, Mobil 1 High Mileage 5w30, 10w30, or 10w40. There are plenty of diesel oil fans on here, so a 5w40 oil isn't that bad.