Hi killer b,
Found the same when I did the front axle on the 3520... I suspect it's the manufacturing process that particular subcontractor uses... or I should say their lack of clean-up/deburring/polishing during production...
An option is to fill the front axle with kerosene and drive around for a bit with the
4wd to stir things up, then drain... could repeat even if you seem to have worked a significant amount of things up... or just go with it (I did).
The 3x20 series seems to have a lot of front seal failure... maybe for this very reason...
If you look at that hydro in the light when you transfer from bucket to bucket, you will notice it "shimmering" from all the particulates from the axle, shaft, & gears wearing in too... bound to lose that kind of metal.