Muncies never had a seal at the front bearing - lube that made its way through the bearing was deflected by the nut, ran down the inside of the flange on the bearing retainer, and drained back into the case through the drainback hole. Make sure the bearing retainer gasket is installed correctly and isn't blocking the drainback channel. Many report that running the lube level about 1/2" below the fill hole (instead of even with the bottom of the hole) minimizes this issue.
