I think I got this idea from UnDummy...I did a recommended flush of the transmission at 30K miles with Motorcraft Mercon V. Then, I went home and die a pan drop and clean, where I put 4 quarts of Mobil 1 ATF Multi-vehicle, with a Mercon V spec. Then, every 10K miles, I've been draining about 2 quarts out and replacing with 2 quarts of Mobil 1 ATF Multi-vehicle. I just hit 60K, so, I did a pan drop to see what it looked like....it was a waste of time...it was pristine. I think I'll keep draining/refilling those 2 quarts until the time it is recommended the filter be changed....I think that is over 100K miles. Highway cruising just doesn't produce much junk in this transmission...