Hello. Hopefully this is of help to those who also have stripped/unremovable fill plug on M46/47 tranny and therefore have to fill thru the drain plug hole. I used a 1/2" flare(not NPT)fitting with tube/hose fitting attached to it. While 1/2" flare size won't screw all the way in it does tighten in fine enough. Never did figure outthis plug thread size. Probably metric 12mm ? Anyway 1/2" flare size worked good enough. Then worked 1/2" clear(so you can see what you are doing)tubing up thru engine compartment where it tightly fit into funnel which sat atop engine compartment. Poured 3x quarts of tranny fluid(in my case Redline MTL) in slowly 1x quart at a time. Takes a few minutes. 3x quarts is slightly overfilling as is recommended here at Brickboard. Not a single drip at all. Then working from underneath car quickly removed fitting from tranny drain plug hole, quickly covered with my thumb, then quickly screwed drain plug back on by hand, then tightened. Lost maybe 3 to 4 ounzes at most. Hope this helps and gives another approach to this job. Lowering tranny to fill thru reverse light switch just seemed to much of a pain and after numerous attempts with numerous tools stripped fill plug still did not budge.

This is one reason I always remove the fill plug *first* before removing the drain plug on transmissions, etc. It isn't fun to empty a transmission or differential only to find it impossible to refill easily!