I'd guess the reservoirs are separate. The pumps run on a common shaft, with the ESP pump in front of the PS pump if they are like the ones on the W124 TE.
PS fluid will go into the res. on the pump, fluid for the leveling system into the plastic tank on the fender, again if this is like the TE.
Make sure you put the PS fluid in the PS pump reservior, NOT the leveling system.
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!