I agree that it is better to change out old fluid, rather than leaving the old stuff in.

I drop my transmission pan every 20,000 to 25,000 miles and clean the filter. Just a little black film in the bottom of the pan. This method drains about 4 quarts of ATF fluid.

Luckily, I added a genuine Volvo automatic transmission cooler back in 1993, when the car had 60,000 miles. The unit drops the temperature 28 degrees, in the summer time.

Heat is one of the main factors that kills automatic transmissions, and I am at 352,808 miles, on the original transmission. I'm sure my fluid change intervals are pretty conservative, but I'm all for cheap, preventive maintenance.
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If it needs to be maintained, repaired or replaced on a 1990 240, I've probably done it. '90 240DL, 352,808 miles, will she make it to 400K ?? >>You haven't really worked on a car until you draw blood<< :-}