I just got through rebuilding a 1980 S12S. Perhaps they are the same. The cone did not have flats on it but the axle was grooved and there was a washer between the locknut and the cone that had a tab that fit into the groove in the axle thereby keeping the cone from moving when you tightened the locknut. To regrease, you hold both locknuts with wrenches and turn until one comes loose. You can then remove the locknut and cone by hand. The little dust cover on the hub pries off with a small screwdriver (careful not to bend it) remove the balls, turn it over, pull the axle out and remove the dust cover on the other side to take its balls out too. Clean, grease and reassemble.