It looks like the plug is for a 3/8 drive breaker bar or ratchet but mine was hard to turn and the ratchet slipped out and barely stripped the fitting. I might have another chance to break it loose before it is totally stripped question is what to use to break it loose. Penetrating oil? WD40? Need help cause I know I leaked out half a quart of Dextron II and want to replace it. Also where else would I be able to put in fluid, under the shifter? Thanks.

 

might want to dig around in the recess and make sure it's clean so your breaker bar fits fully into the hole.

 

I hope the one you're messing with is the upper one on the passenger side...
All the ones I've seen have a square head on them that you can fit a wrench onto, although the later ones could be different.