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I would drain the lube then pressure test the drive to 11 psi. The areas for concern are the drive shaft seal, water pump seal, propshaft seal, yoke seal and the shift rod seal.
The immediate seals you can see are the propshaft and yoke seal. If it does have a leak and you don't see anything visual that leaves the other seals. I would just reseal the entire drive. If one fails the others could be right behind it.