500SE Power Steering Fluid Leaking...

My 1987 500SE found fluid leaking from the oil reservior's upper connecting pipe (a steel pipe connected to the reservior and other end joint with the rubber hose). Had tried to tighten the nut at the reservior side but still found moisture of fluid leaks from the reservior's side (at the connecting nut) after driving. I was wonder if the connector between reservior and steel pipe contains seal O ring (in this 1987 model) or just direct coupling? Any idea how to fix? TKS.