Diff. leak source

[Italchic]

Well I found the source of the leak in the differential. Turns out it is not the gasket but the pinion seal. Since the shop manual says replacing this can be complicated, requiring special tools and replacing other parts as well; and since its not that bad, I'm just going to keep an eye on the level of oil, top it off every so often and, as others have suggested, live with it until such time that it is absolutly necessary to replace.