The pin in the aft side of the nut is for the retaining wire for the nut to the stem. 99% of the time, if you get a leak through the wire the nut is loose, or the flares are not making good contact.
Being thats an old 701 hose thats been in service 17 years, you might think about replacing it.
Tom Swearengen, TS Flightlines LLC, AS Flightlines
Joint Venture with Aircraft Specialty
Teflon Hose Assemblies for Experimentals
Proud Vendor for RV1, Donator to VAF
RV7A Tail Kit Completed, Fuse started-Pay as I go Plan, on hold while we develop new products for RV builders