I finally got around to my hydraulic system. Found the dip stick, filler hole and filter. I removed the filter but no numbers are visible. Did a search and found a Wix and NAPA number, so that will be easy to take care of. It was quite obvious that the filler hole had not been accessed in a very lengthy period and the oil was down halfway on the dip stick, and actually looked clear and fresh, so my question is, does Hydraulic oil dirty up like engine oil, and what should I be seeing or looking for to determine oil change frequency? The original tach/hour meter reads 1486 hrs, but does not work so I have no idea of correct hours. I have installed an after market hour meter, very easy install, and have 12 hours on it. Does extended use of the hydraulic oil have a negative impact on the function of the cylinders?