86 560SEL 53K

I've put 3 litres of MB hydraulic fluid in the suspension reservoir today. It's empty again. Where is it going?

I see no leakage up front. I've looked under the rear, although not really under, just what I can see from looking under the car and hands and knees and see no dripping.

Must I use MB hydraulic fluid or will any hydraulic fluid work?

Also, when the car is running, I hear a hissing from under the rear near the passenger rear wheel.

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R Martin
Dallas, TX (Addison)

86 560SEL, 128K