damian........while there is a gasket on the lower 3-point link, the lower link is actually held inplace by a BIG nut INSIDE yer axle trumpet cotter keyed and torqued to 150ft/lbs. It should be intuitively obvious, you will haffta remove all 10-nuts that hold the axle trumpet to the diffy.
NOTE: the 8N has a taper'd lower link pin that semi-solved the "leaking" problem, but it still can be wallered out.
While JB Weld is good stuff, you will haffta drain 5-gals of hydro-tranny fluid and CLEAN the trumpet hole so the JB will stick and cure. Many times the lower lift hole is WALLERED OUT and the ONLY way to seal the no long round hole is to J&B it. (still torquing the inner nut to 150ft/lbs)
I saw a sign the other day, "Harleys don't leak, they just mark their parking spot". Yer 9N is marking it's spot. Iff'n it really bothers you, a clever shadetree mechanic could figger out a way to bailin'warr a tuna fish can to catch the drips. As long as you have at least 4-gals of hydro-tranny oil, yer good to go. ........dripless Dell