A good quality hydraulic oil should be what you need. These Jinma steering systems are straight hydraulic – using a hydraulic cylinder rod movement to turn a steering knuckle and hence front wheels.
Depending on where you are would influence the oil choice. I live in an area that frequently gets -30 F temperatures in the winter. For me the hydraulic oil I use is AW32 – the AW46 is too thick at these temperatures. There is a noticeable difference between the two oils at start up operation.
HTH
mariner