The earlier AW4's do not have a TC drain plug, and I suspect this is true of all years (although I can't confirm it offhand.)
Apparently, the "power flush" is the only way to clear all the fluid - but I've not had any trouble with "service changes" of fluid. It's not generally necessary to change the filter, since it's little more than a sump strainer (open mesh stainless screen.) On all my XJ's, I've only pulled the pan the first time I changed the fluid, then every time after that I've allowed the fluid to drain over a nice, strong magnet (I have several) to check for metal particles. If I don't see any, I reseal the plug and refill.
I plan to add spin-on remote filters one of these days - I'm just not in a huge hurry (and all four of my XJ's are now slated for long-term restomod projects, so I can do it all at once anyhow.)
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