I did a service on the k46 transaxle on my rider and the oil was black, black, black. I don't have an hour meter, but I estimate it had 400 hours on it. I refilled it with Mobil 1 15w-50. I should probably do it again in a couple of years as I mow a hilly back section and have ATV tires on it in order be able to do so.
As for the oil, Kawasaki recommends 10w-40 for the FR651V. Why John Deere does not follow Kawasaki's recommendation, I don't know. Personally, I'd probably use 15w40 as I always have some on hand.
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