I wouldn't be too quick on replacing the banjo fitting (part #15). It certainly looks to be solid enough. Or maybe just the hose has failed ?
The mfg. drawing shows two washers (parts #23) at $22.30 ea.
! Your photo shows only one gasket on the bottom joint and maybe no gasket on the upper joint. Remember, the photo is upside down. The one gasket showing is definitely not the $22.30 trophy gasket (#23) but still looks like a healthy substitute.
I got two nickels, a dime and a ball of pocket lint that says that's where your problem is. It's held up for years and finally got shaken loose. You need to insert a 5¢ nylon gasket from a hardware store in that upper joint. During cold weather, it helps to heat the banjo assembly with a hair dryer when tightening. With a heat gun, be realllllllllllllly careful.
When you're working on that assembly, whether tightening or loosening, always hold the upper most nut as a backup. Maybe there should be a gasket up there as well.