4300 service manual says change engine oil and filter every 200 hours, which seems a little long. I use high grade synthetic oil, but tend to change it after 100 hours or so. It also says change hydraulic oil (HST) every 200 hours, which seems totally unnecessary. The hydraulic oil and filter was changed at around 200 hours, but that was because the rear axle seals leaked and the tractor had to come apart. I now have 790 hours, the oil is clean, everything works fine, and I have been told by friends with big farm tractor experience to leave it alone. I realize it's not a big expense to change the hydraulic oil, but it is a bit of a pain. Comments?