I am going to trace the leak this evening. Yes I actually purchased from the original owners son and he had the original manual with it.Hi and welcome aboard!! Follow that leak, see where you can trace it to. Could be a simple oil gasket change in side the shifter cover - just a few bolts to pull that off, clutch cable routes to it - pull that back, and see if you see a load of fresh oil in there...then clean, and replace the oil seals there...I am picturing that your motor layout is not far off from the other twins of the 70's...do you have a manual yet???
Oil seal it was. Local bike shop had the seal you listed and just got back from a ride to the lake with no smoke and looks like the drip is gone. Thanks!!Welcome to the forum. Great to see another 400 series here. That oil drip could be as simple as the airbox oil drain. Check the hoses on the right side near the center stand. And yes, the shifter seal is common, but not on clutch cable side. It is in front of the front drive sprocket behind the alternator cover on the left side. Part number 91204-425-003.