While putting in a new fuel filter I noticed my transfer case is quite grimy. I couldn't see the source of the leak, so I positioned my camera as high as I could and shot a picture looking back down at the top of the transfer case.

I'm going to clean it up in the morning and check fluid levels, but I suspect the source of the leak is right there at the port into the case. My question is what is that black thing bolted into the port? It looks like there is an electrical connector hooked into it, but then then exposed circular opening has me confused. Should something be there? There is a corrugated line barely visible in this picture beneath the electrical connector. What is that?

I'd like to know what these things are before I take them off. Especially since I'm not currently having any issues (at least that I am aware of).

Thanks for your help!

Happy 4th of July everyone! To all our armed forces -> .

 

Taking an educated guess here: speedometer gear & sensor?

 

Bingo. Transfer case speed sensor..

 

That looks like its coming from the output shaft seal as well.