This response might be a little late but; one other consideration is the fact that many an axle bearing failure has actually been the result of a seal failure first.
In the 9 inch Ford unit which uses the sealed ball bearing (not all do), along with keeping the gear lube off the ground, the seal is responsible for keeping the lube from entering the bearing, diluting the grease and causing it to migrate out of the bearing assy.
The gear lube witnessed as a leakage has two routes in its' escape once passed the seal to be visible. Either around the alxe bearing's outer circumference, between the O.D. of the race and the I.D. of the housing, or thru the bearing assy. itself. In the prior instance there is no effect on the bearing assy.; in the latter, the grease is liquified and "washed" out of the bearing causing failure do to lack of lubrication. Note: that although the definition applied to the bearing may be "sealed", this is understood as a grease seal for the retention of the grease for lubrication about the bearing, not as a capable fluid seal for retention or separation of gear oil.
This is another one of those "things", that with experience, and a developed "feel' for how things should be, one is able to decide, "Ya or Nay" to the serviceability of.