[Tony Smith]

It's likely that, but another less likely possibility it could be leaking around the cover for the Oil Pump idler gear.

These covers are one piece casting with the Idler Shaft pressed into the cover, but I have seen some where the shaft is a loose enough fit that oil can weep past it.

Also, the original gasket for the cover partially covers the grub screw in the end of the Main Oil Gallery. This grub screw should have been installed with a thread sealant, but if not, oil can weep along the thread (this gallery sees full engine oil pressure) and be lost where the gasket does not cover the screw.

There was a later modification of this cover and gasket to include a hump that completely sealed the grub screw, but unfortunately most modern gaskets don't have this hump, so the problem still remains even with the modified cover.