I have a 2010 Flex with EB and the 6F55 transmission. I'm swapping in a used transmission and a reman torque converter because the torque converter clutch failed at 150k on the odometer. The transmission has a sealed case and a non-serviceable filter. I would suggest two steps you can take now. First, do a couple of short cycle drain/fill sequences to clean out the old Mercon LV - there is a lot of discussion about alternatives to the OEM LV fluid - I would suggest sticking with the OEM Motorcraft LV stuff it if you want a fluid that is certified to meet the OEM specification. There are a few other certified fluids out there, but the OEM Mercon LV is synthetic, considered to be stout, has the OEM additive pack and the dark color does not mean it is actually "worn out". Despite many folks having good success with products like Maxlife, my personal preference is to use fluids that are certified, tested and licensed to meet a required specification. Maxlife is not certified and licensed to meet the Mercon LV specification. Second, consider adding an in-line transmission fluid filter. I've decided to keep things simple on mine and I'm adding a Magnefine inline filter (1/2" ports) on the return line from the transmission oil cooler. This additional filter will help trap smaller particles too small for the internal filter and also help prevent that filter from clogging. Alternatively, you could install a remote transmission filter if you are so inclined.
One other word of advice. If your Explorer is AWD, then it has a Ford PTU in it. Make sure to service that PTU regularly (every 30k or so). I would suggest using Mobil 1 75w-140. Also, if the vehicle has more than 30k miles already, you should exchange the PTU fluid before you do anything to the transmission as the PTU is the higher priority by a very large margin.
Good luck.