Mainshaft Seal
If you're working with an early transmission (prior to VIN 24196) you'll need this oil seal for the mainshaft. It seals between transmission and transfer case, preventing oil migration from one case to the other. (optionally, you can use a sealed, not shielded, rear bearing).
It fits in the bearing retainer, and seals on the bearing spacer.
Chicago Rawhide #17310 (see sidebar, shown w/bearing spacer inserted)