Below are some links to where I get most of my wood splitter parts. I have splitters that have been in commercial production for decades and the parts rarely wear out. A log splitter is usually made from very strong and durable components.
Hydraulic Wood Splitter Parts
Since hydraulic log splitter parts operate in a constant supply of hydraulic fluid, they are always kept well lubricated and away from the influence of moisture. This allows hydraulic components to last for a very long time compared to many other types of mechanical components.
The hydraulic components of a wood splitter consist of three main mechanical parts. A hydraulic pump, a hydraulic valve (control lever), and a hydraulic cylinder. These will by tied together by hydraulic hoses and will include a filter and a hydraulic reservoir.
Of the major parts on a hydraulic log splitter, the engine is often the first that will wear out. I have gone through several engines before ever needing to replace any hydraulic components. The second most likely to wear out is the hydraulic valve. Either the centering spring will break or the valve will start to leak. Although they can still work for a long time while leaking if you don’t mind an occasional drip. I have never had to replace a hydraulic cylinder or pump.