I do this type of flush as well. I changed the filter on the FIRST fluid exchange but not after that. Mercon V has friction modifier and needs to be changed. If it isn't burnt or really dark I'd go for it. These transmissions are pretty beefy.
'04 Silver Marauder w/ sunroof - HID lighting, JL Audio / Eclipse DVD/NAV/iPod/camera, 4.10's, 2" drop, Progard Bumper Baffle, Delete tips, Billet Pedals, BC4E dead pedal, Lidio Tune, Mach1 chin spoiler, K&N CAI, TCE lines, Super40's, tinted tails, SS Inserts, Heinous Control Arms, Real oil gauge, lighted door handles. Currently installing Eaton M112.
2004 Mercury Marauder
Born March 2004, adopted October 2005. Sold January 2012, adopted AGAIN January 2016
2,187 of 3,214
997 in Silver Birch
448 with light flint interior
304 with heated seats
336 with sunroof