Some important tips to consider when working on any hydraulic system:
Never work on any piece of equipment until you have ensured that it is locked or tagged out. Don't start disassembling a piece of equipment until you have diagnosed the problem and planned a maintenance procedure. Take time to look at schematic diagrams and service bulletins in order to get to know the system you are working on.
Operate the system yourself to check for system pressure, oil temperature, smoothness of controls, unusual noises and smells, and oil leaks. Visually examine hydraulic fluid for signs of trouble--dark fluid indicates excessive heat; milky fluid means that there is water in the system; foamy fluid results from air in the fluid. Release hydraulic pressure before beginning work. Always assume hydraulic pressure is present, even in systems that have been idle for several hours. Cap or plug all lines and ports upon disassembly to prevent dirt from entering the system. Don't check for pinhole leaks with your hands. High pressure hydraulic oil can shoot from a leak at a high enough pressure to inject under your skin. Do not modify a hydraulic system unless you know what you are doing.