Easy test: With engine @ idle; unscrew fill cap in reseviour, and slowly lift it up. If retuning fluid is foamy, one on both accumulators are ng. (Nitrogen gas in an accumulator is mixing with the fluid).

The cap contains a replacable filter (white plastic cylinder). It's the return from the controller (mounted in front of gas tank).

The feed comes from the COMBO power steering / self leveling pump. Hose from bottom front of pump goes to bottom of self leveling reseviour. If it hasn't been replaced, its time is due. Easy diy. Fluid should be clear, not black.

NOTE
FEBI 2615 into self leveling reseviour.
FEBI 08972 into power steering pump.

Bob