I seem to have a gearbox oil leak around a plug on the gearbox. Shown in the image below with a red arrow point to it. I was thinking that's the speed sensor, but I'm not sure if it is. Could it be leaking from here, definitely seems to be a build up of oil here for sure.
What do I need to replace, o-ring, gasket? I didn't want to just take it off and piss out all my gearbox oil.
Advice would be much appreciated.