Those are the projections for the shift fork rails. Two stamped sheetmetal "cups" that have a very slight taper to their profile. They are tapped into place in the case. When installing new ones, I place a very thin film of hylomar on 'em before installing.
Spicer refers to those parts as: "shift rod cover (thimble), p/n 18-59-2.
The open end of the cups have a slightly raised/increased profile where formed, that raised portion is what creates the seal when installed in the case, similar to installing a cup plug in an engine block.
Also, make certain that the vent for the tc is open and can "breathe". If it's not vented well, oil leakage from any penetration will be a continuous problem.