The procedure for selecting the correct number of ball/bell-collar seals is nicely described in the Shop Manual. How did you go about selecting how many seals to use - too many and you leak; too few and you loose the ability to easily move/rotate. This location should not leak much (no more than a few drips every time you stop).

Another common location for a little leaking is at the collar/cover at the rear of the u-joint ball/bell. The seal at the rear of the collar, around the torque-tube, seems to be a place to expect a few drips at every stop.

The u-joint does receive lubrication from the transmission; however, people have reported using the separate fill hole (that you describe) as a way to put a little lubricant into the ball/bell.

Did you check to see that the bottom edge of the valve cover produced a flat surface all around the base, and were the areas around the screw holes in the valve cover flat or indented downwards? I cement the valve cover gasket to the bottom of the valve cover.