Oh Lord, Tinmann, I guess if you're a new member, we'll forgive you for bringing up this topic again/w3tcompact/icons/laugh.gif. It's been beat to death on the old board and you might want to go back to the archives and read some of those messages. There are a number of people convinced that you should use synthetics (especially Amsoil), and there's no doubt they're good. I just happen to be one of those who are not yet convinced they are worth the extra cost. The most popular oils in my area are the Delo 400 (15W-40) or the Rotella T (15W-40), and I, along with all my neighbors and brothers, use the Delo. If you bought the tractor new, it should have a manual with the service intervals specified, and I'd stay with them; especially the first 50 hour service. In the hydrostatic transmission, I'm using the Kubota UDT, although the semi-synthetic? Super UDT is undoubtedly good, for more money.
Bird