Transmission fluid leak -- 99 Elantra

Hello everyone,
    While working on the car yesterday I noticed transmission fluid leaking from the top of the transmission housing on my sister's
99 Elantra. The leak is located to the right of where the upper and lower radiator hoses are located. I have taken a picture of the leak
From what I can tell it looks like it is coming from a cap underneath the wire in the picture. So it looks like it's going to be a lot of removing to get to whatever is underneath it. Does anyone know what that part is called and is it a gasket or something else that's causing the leak? The car unfortunantly is at 106k miles so I'm out of warranty on this and hoping to fix it myself.
Thanks in advance, Nick
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