First off, hello everyone...I'm new to this forum.

Also, I am new to the diesel world and am wondering what this is. I've narrowed down a leak to this - it's the black wet "L" shaped tube. It's leaking out of the end where the connection meets up to the tube.

Any help would be appreciated!

 

That's your trans line going to the heat exchanger. Take off the clamp and put a regular hose clamp on it!