2 things, there's a seal in the front retainer that may have been missed and should have been replaced.
The more likely thing is the snap ring around the bearing was not replaced with the original one from the original bearing.
The snap ring that comes with the new bearing is often not narrow enuff to fit in the recess in the retainer, and will not allow the retainer to seat against the trans case, and often damages the retainer when bolts get cinched down,
Replace/grind snap ring if nec.
If so, check for cracks around retainer bolts.
Good luck
