3-speed auto with torque converter (vs. hydraulic clutch) as in my 1973 450SE: purportedly very rugged in both design and service?

Other than the normal Mercedes-type tranny service with filter and drain of the torque converter, is there anything else I should be aware of or do to keep it running? Seems to me that it shifts pretty darn good, nice and smooth, no slippage I can detect.

Is it worth going to a synthetic tranny fluid or will a conventional DEXRON III/MERCON suffice?

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'91 420 SEL @ 199K, '92 SVX @ 181K, '93 SC400 @ 86K, '93 Kaw ZX-11 @ 30K, '87 F250 @ 181K , 2001 Valkyrie Interstate @ 6K, Y2K Honda NightHawk 250 with 1.5K, '88 420SEL I.@ 179K & the 2nd latest, an '88 420SEL II.@ 210K runnin' parts car, '85 F150 300/NP435