uncheels

I've got a auto-tranny leak that happened all of a sudden, no warning. I've found the exact spot where the leak is but I'm not sure what is involved in the fix. I have a Chilton manual, but it doesn't tell me what the part is. It is a round cylinder shape facing the radiator right in between where the cooling lines come out the bottom and a pan that is at the top. 1st - what the heck is that, and 2nd does it come out some how?

**Click on gallery to see a picture of the part I'm talking about.