Water leak question

If water is leaking from that bolthead, then that entire bolt-tunnel has water in it.
No matter whose advice you follow, that cover has to come off.
From my memory, there are only a total of three bolts that go into the water jackets, and that ain't one of them. but I could be wrong.
In any case, you gotta figure out how that water is getting into that tunnel, and STOP it from happening again; else you may have a dickens of a time getting the cover off at a future date when the tunnel is filled with corrosion..