[elmariachi]

I wouldn't overdo the grease, just enough so that the axle can slide through, but no excess. When the axle arrives at its final resting place, that seal rides around the smooth, flat surface just behind the birfield joint, where it only needs a thin film of grease. When inserting the axle, you need to lift up on the entire assembly, relieving as much weight as you can on the seal as you slide the shaft through. Only at the last minute will the seal see some slight pressure as you press down on the joint, causing the inner end of the shaft to slide up and into the 3rd member.