I'm going out on a limb... (not a limb at all)
Why would honda design such a thing with no threads, no hardware in the diagram.
I wouldn't plug it, but rather figure out why it was designed to weep?
What is it telling you is going on with the engine? Has a vital seal failed and this was designed, like many engineered indicators, to inform the owner/maintainer of an imminent failure?
Far too much went into the design of this right hand cover to just plug it and run it. But, i'm sure plugging it will stop it from dripping. -BIG DAN