I've always heard the theory that you should periodically use the air conditioner even when not required, to keep the lubrication distributed. Maybe this helps keep the o-rings moist with lubricant too.

So mine get some activity right up until the bitter cold months when it won't turn on due to the ambient temperature sensor.

Ken300D

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1982 300D at 351K miles
1984 300SD at 217K miles
1987 300D at 370K miles