Engine: JDM B16A First Gen, Stamped '91 and bought from HMO

Alright folks, when this engine was in my crx and started to leak oil i took no chances. i used it as a reason to change all the gaskets and change my water/oil pump but STILL oil was leaking. So I decided to take the engine out of the car and while looking around i noticed a little oil hanging around near this hex bolt:



I used a turkey baster to drip water on the area to see where it would drip and sure enough the water leaked behind the oil pump and dropped down all the way to the oil pan gasket giving the impression that the problem was there...

Can anyone tell me what this Hex socket is for and whether this can be prone to leaks. There was no gasket and it was screwed on pretty tight but it came off without too much of a struggle..

 

anyone!?

 

could use an o-ring, if not its just a plug, seal it with some hondabond and put it back in.