In addition to pouring a little fluid in every couple of miles, I recommend staying out of the throttle and allowing the tranny to shift early. Try to keep the engine RPMs as low as possible which will also keep the RPMs on the power steering pump as low as possible.

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08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280