Yesterday I was working on my trusty old pickup hoping to do a header instal. First order of business what to pick up the sawzall and go to work on the old rusted exhaust. once I finally cut thru the first pipe I accidently bumped this brass-ish diaphragm looking piece with the saw and now I’m leaking tranny fluid all over the place.

I need to replace this but I don’t even know what it is. Any help would be greatly appreciated.