Leave it for now. If it took a few weeks to become an actual drip or two, its no biggie. I actually consider leaks of this type to be an asset as they add a beneficial anti corrosion film to nearby parts.
To answer, I agree with the pan arch or rear main. Pan being more likely IMO.
As a data point from someone not on the list. The black is cleaner in theory, but as stated - silver matches the expected look of an OEM fitting much more than fancy shiny black.