The power steering pump on the w140 with self-leveling rear suspension is termed a "tandem pump". One half produces the pressure for the steering and the other half for the rear suspension, but share a common reservoir of hydraulic fluid. The two sides are independent and produce/maintain different pressures. Keep an eye on the reservoir fluid level, as a continuing loss (of level) could mean a problem with one or both of the rear accumulators, which can lead to hyper-expensive repairs unless addressed before physical damage is done. I learned about these things the hard way about 6 months ago.

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1996 SL320 97K miles
1996 C220 130k miles
1992 500SEL 170k miles <---sold
1986 300E 216k miles <---sold