Couple oil questions here. Spent a lot of time lurking before I bought a machine. A lot of good info on this site. Just picked up a Hustler Z 25/60 for non commercial use. Have about 6 acres of my own and 2 for my mother to mow, possibly pick up my in-laws with another 4. Very pleased with the machine so far (4 hrs.). The Hustler manual says change oil every 40 hrs and then has footnote that says follow engine manual. Kawa engine manual says change oil every 100 hrs. Which is correct? Second is about the Hustler super oil. At about $12.50 per Qt. it is about twice that of Mobile 1 or Amsoil full synthetic. Other than the doubling of the engine warranty, what are the advantages of super oil. Is the synthetic acceptable, preferred, or not recommended. Don't mind spending the money for the super oil if there is a good reason.