Mine was leaking from this area too. The fix was to replace the O-ring on that high pressure line.
I bought the O-ring from the Ford dealership for $2. You can also try to tighten that large nut with a 15/16 wrench, but I DO NOT recommend it, as the reservoir plastic might be brittle and break.
I made a video of the repair in my early days of YouTube repairs (3 years ago), the video is Ok compared to my recent standards, but it gets the point across.
View: https://www.youtube.com/watch?v=7ex-Z-DzfUs