Welcome to the past! There is a slip ring over the Belt Pulley shaft that has no seal nor any interior means of remaining in place . . . unless you mount a belt pulley or a casing. You can get the slip ring from CIH if it is missing. The casing can be fabricated from a section of old chain link fence top rail of the 1" size. Use a plumber"s rolling cutter and cut the rail 2" long. You will need the end bolt and washer to hold it on. The new fence rail sold now is too thin. The oil seal rides over the slip ring and limits the oil that can seep out at this point. There will be metal shims here behind the bearing and seal mounting to fix the clearance of the gears. IH provided no seal for these shims except the close spacing and paint over the outside. It was expected to leak oil and they all do. I did put a bit of form-a-gasket between mine but the space between the slip ring and the shaft has no oil seal. It will leak. You can pack the slip ring and shims in with some heavy weight grease and reduce the leakage but it will not stop.
Otherwise, do not overfill the transmission since none of the seals will hold standing oil. These seals were made to minimize oil loss not stop it.