I have a L4600. It is 15 years old and has about 200 hours on it. I did a hydraulic fluid change at 5 months, 10 years (about 100 hours), and 2 yrs ago. Even though it is not called for until the 400 hour mark should I change it again. The tractor does not see much usage but is in AZ where it gets over 100 in the summer for months at a time.