There are actually THREE seals you'll need for the front spindle, here with the factory part-numbers:
1. Inner wheel-bearing seal: J535 9703/National #471271 (#37 in your diagram)
2. Stub-shaft flange seal: J812 7350/ National #722109 (#51 in your diagram)
3. Spindle-bearing seal: J812 1397/National #722108 (not shown in your diagram)
In my front spindle reassembly video, you'll see the first seal installed at the 7:35 mark, and you'll see the other two seals in the 9:50-12:00 time-span.
The fluid is kept in the differential by an inner axle-seal (not shown in this diagram) that is driven into the inside of the housing.
As for that leak, that's an interference-fit supported by a plug-weld; a leak in that location could mean a distorted housing or the beginning of a bent axle.