My 2008 Lucerne, 3.8 v6 (of course) has had transmission serviced (full flush every 60 or 70,000…

My 2008 Lucerne, 3.8 v6 (of course) has had transmission serviced (full flush every 60 or 70,000 miles. Now at 250,000 miles it is due for its 4th service . My favorite mechanics are telling me at least 4 different things to do...such as ...nothing, don't touch it...full flush...reverse flush...change with new filter. Color is just beginning to darken but still reddish-pink, shifts perfectly...getting 30+ mpg. Help!

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