When it come to an automatic transmission, changing the fluid whenever you do it, is a good thing.

Another thing is how a person operates the transmission. Personally, whenever I get to a red light, or have to stop for almost any reason; the shift lever by habit goes directly into neutral. The enemy of any piece of machinery is heat. My thinking is that instead of the torque converter sitting in traffic on a hot day generating heat, putting the tranny in neutral reduces heat.

Quick acceleration, (not a problem with W123 diesels) is also counter to long fluid life.

I have gone 60k miles on the same fluid, and it drained looking fine.

Works for me.

Would if I could...can't on the car in question (our Honda Odyssey). All that a DIYer can do is get out 3.5 quarts at a time. In fact, even in the manual, the procedure for flushing is describe in terms of multiple drains an fills.

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14 E250 Bluetec 4Matic "Sinclair", Palladium Silver on Black, 154k miles
06 E320 CDI "Rutherford", Black on Tan, 172k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver, 142k mi, wastegate conversion

19 Honda CR-V EX 61k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife