CRANK A 4H6579 - Caterpillar

Do not check for leaks with your hands. Pin hole (very small) leaks can result in a high velocity oil stream that will be invisible close to the hose. This oil can penetrate the skin and cause personal injury. Use cardboard or paper to locate pin hole leaks.
Check all oil lines and connections for damage or leaks. Check for hydraulic oil on the ground under the machine. If oil can leak out of a fitting or a connection, air can leak into the system. Air in the system can be as bad as not enough oil.
Remove the filter elements and look for particles that were removed from the oil by the filter element. A magnet will separate ferrous particles from nonferrous particles. Nonferrous components could include the following components: piston rings, O-ring seals and gaskets. If the filter is plugged, drain the hydraulic oil and replace the hydraulic oil and the filter.