Pinion seal problems
or a driveline imbalance or angle problem) will kick
the seal around and it can't totally keep up with the
shaft (always behind) so you get some weepage.
Is this a leak just sitting, or a leak only when spun
for a while (driving)? Clean it real good with paper
towels, white glove style, and see if you get a weep
overnight or not until after the next drive. That'll say
if it's a seal/shaft problem, or a wobble / setup one.

