I just wanted to update this thread that the new "Non Flange" pinion seal Car Quest #473448 ($11)worked great in my 56 3100. No need for a jury rigged spacer for the yoke, and the oil deflector fit perfect next to the case without rubbing on the seal flange. Also that the National "sleeve" #99170 ($38) solved the wear problem on the yoke. After topping off with gear lube, two test drives for a 20 mile total, and letting it sit for a few days, NO Leaks! So glad to get this fixed finally, and hope this info might help someone else. As others have noted in the forums here, make sure to use some permatex on the seal flange and the yoke splines as those are potetial leak areas as well.