I'd drop the pan, change the filter and drain the converter. I wouldn't do a flush with a machine. Exchanging the fluid through the cooling lines and changing the filter is ok but not with a machine and flush/cleaning chemicals.

When the fluid looks really bad and the transmission is presenting problems I'd leave it alone. If the fluid looks decent service it and continue to service it on schedule.

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer