You've got an AW70 (or 71, if you've got a turbo). Some 700s even got an AW70L (or 71L), where the L refers to lockup -- nothing to do with the overdrive, but rather with a lockup torque converter to further improve fuel economy.

And these AWs (Aisen-Warner) have no filter. They do have a screen, but it doesn't catch and hold dirt like a true filter -- it just blocks debris, which falls off when the pumps stop, so they stay clean; if you dropped the pan, the screen would appear clean, so don't bother dropping the pan. Your advice, therefore, was essentially correct -- the only service it really needs is periodic fluid flushes, and the best method is the "IPD method".
Rather than the advice you cited (drain and refill the pan with 4 quarts), don't even open the pan. You see, that does nothing for the several quarts in the torque converter.
The IPD method, instead, flushes the whole transmission -- sump and also the torque converter -- but obviously, it means you have buy more ATF!
The IPD method means extracting the fluid through the radiator fitting, and refilling through the dipstick tube, 2 quarts at a time, over the course of 16 to 20 quarts (especially if you never did it before). And synthetic is recommended!
If you're interested, write again and I'll give you the exact procedure -- it's very clean (you can wear a white dress shirt without much risk, not needing to get under the car) and very easy. You just need the right hose, a clamp (or else buy the IPD kit), and the right funnel.

As for a cooler, you of course know that it is already cooled, passing through the radiator (an oil-to-coolant heat exchanger). In 240s, you don't need any auxiliary cooler unless you tow a big trailer -- I tow one of my smaller boats, so I have one, but do you do any towing? And your 700, btw, has the same transmission as 240s have.

Lots of folks on this forum have seen their original transmission last 200 to 300K miles (allowing that folks on this list take good care of their cars, more so than the general public). The main problems are some leaks, especially tailshaft leaks, but the transmissions live long lives.

And of course (as I mentioned earlier), I recommend synthetic ATF as the fluid to use.

Good luck.

By the way, feel very luck your shift quadrant isn't PRD321 (without any overdrive button), because that indicates a different transmission that is notorious for self destructing (it overheats if your rev the engine in neutral, like during a non-dynomometer state emissions test). Never buy a car with that!