This AM the paper towels I wrapped around base of tube and left in drip pan were nicely soaked.
After wiping tranny dry, one drip falling every 15 seconds or so into the catchpan.
Went to Ace hardware.
3/4 inch OD 0.10 thick O ring.
33 cents each.
Drained just over two quarts into a pristine drip pan, then put it into a clean container.
A paper towel on top of tube stayed white and dry, but when I pulled tube lost perhaps 1/4 more quart into the returned catch pan
Easily removed O ring from tube. and cleaned inside bore, with Q tips, then drained 1/2 to 3/4 more quarts of fluid.
The bottom of the drainpan with this second draining had some debris in bottom, compared to the first draining, which had none.
So pulling the tube, despite measures taken to sterilize the exterior before doing so, still allowed some gunk inside, which drained out.
All hail the drainplug whose bung is welded to exterior of pan.
New o-ring installed and tube seated, I returned the first 2 quarts I drained, the second fluid from second draining, I left out.
No leaks.
I have a new quart of ATF+4 ready to go once its warm and parked level.
I think I'll consider replacing the O ring at future TX fluid changes, rather than wait to find a puddle.