You can use just about any oil marked Diesel that has from rating of at least CD. You may go up, CE, CF etc. Here's a good article on diesel oils. John Diesel oils
I USED it at the 50 and 100 hr service...and most likely will USE it at the 200 hr too...so i guess you can say I USE it... /forums/images/graemlins/grin.gif
I personally wouldn't use anything less than 10W40 in warmer weather, and do use 15w-40. The only real advantage I see in the synthetic is if you're not going to use the tractor and change the oil often enough to avoid chemical change damage. Regular oil I would change every 4-6 months regardless of use, but with synthetic, that would not be neccessary. The owner's manual does not have anything at all about synthetics, but they do recommend 10w40, no 5w. You might right to customer_service@kiotitractor.com and ask them about it. John