Howdy,
OK, you have the correct line. Did you have any issue with any of the tees? could there be a hairline crack in one of the tees? Since this is the fuel return line. There is not a lot of pressure in the line making it come spraying out. That in itself make it hard to locate the point of failure.
Yes, it is one of the things that need fixing. Otherwise it will just coat the compartment with diesel fuel.
OK, in the one picture where you are pointing to the exhaust area. What are you pointing to? If that is black oily goo, your engine is wet stacking. That means it has been run lightly, and the unburned fuel has been building up in the exhaust.
Run the unit long and hard with a good load.