What is this part called on the automatic transmission?

I have a leak that appears to be from this plastic piece where the automatic transmission mates.

Any help with what this is called or insights as to the problem is much appreciated. This 4runner is a 2006 SR5 232K miles. I had the transmission fluid and filter changed about 20K miles ago, and there have been no issues until this leak.

 

Pretty sure the plastic piece isn't whats leaking.

Might want to have the rear main seal looked at.

 

ok that sounds worse for sure

 

If it is the rear main seal, its not 'worse' mechanically, just a seal that needs to be replaced. But the transmission will have to come out to get to it, which does make it financially worse, lol.

 

yes worse financially is what I meant. At least it’s paid for