Hydraulic fluid/Power Steering fluid

Hydraulic fluid/Power Steering fluid

Power Steering fluid/ Hydraulic fluid level

My 1991 MB 560SEL makes noise when I turn right or left when driving. I think it needs Power Steering fluid. However, the Owners Manual only mentions Power Steering fluid but doesn't say where the fluid goes and how much to fill. It only states that it needs 1.4 quarts. Neither does it say how much Hydraulic fluid should the Hydraulic container have in it and to what level. There is a wire around the container (which has a small knob on top) and it appears that it is full to that wire but the container seems only half full. Is the Hydraulic fluid and Power Steering fluid one and the same? I'll have to see if I can buy some online but where? I don't live anywhere near a MB Dealership and I look forward for some information. Thanks!