I can't quite tell by the picture exactly where that is but I've read; speedo cable exit spot can leak, gear shift linkage input spot, drain plug.
I've suspected gearbox leaks before only to realize it was oil leaks getting blown onto the bottom of box and dripping there, my latest one is most likely another cam box gasket leak that runs down the front of the engine, gets into the slipstream and eventually drips from the bottom of the gearbox. I'd advise cleaning it off, dusting everything with some baby powder/talc of some sort, drive, park, check.