Mercury Repair Questions? Ask a Mechanic for Answers ASAP
In my opinion you should have the full flush performed. Make sure the shop knows which fluid to put back in and how to check the level correctly. Most transmission shops do, but some of the quick lube shops are not as good at it since it's not your typical transmission. With 53000 miles there is little risk of causing a slipping problem as I mentioned before.
We have about 30 of the ford explorers with the same transmission in my fleet and they are killing off transmissions one by one because there was no transmission fluid replacement performed on them in the past.
Since I came on board with them two years ago I instituted a transmission flush schedule and ordered a new flush machine for the shop and we have had very few transmission failures in the last few months which to me indicates the flushes are preventing failures.
I don't want to make you worry, those explorers that are failing all have over 120k miles on them.
You shouldn't need to worry about your transmission failing and time soon, especially if you start performing preventive maintenance now.