Sorry it has taken me so long to respond to you. We don't put too many miles on our UA per year so I change the oil once a year. I change the tranny fluid about every other year. I have not had any problems and my oil analysis looks good.
Paul

Purchased a 2000 40J UA year ago Cat 300hp my mileage is between 7 to 9 dependig on the wind, tell me how ofter due you change the oil, I'm using dello 400 bot my change.