How much would an American-aligned unified Korea threaten the Soviet Pacific Fleet at Vladivostok?
Short answerIt would add pressure but not become a decisive new threat, because Japan already created a similar problem and geography limited direct access.
NotesThe Soviet Pacific Fleet already faced nearby American-aligned Japan, so Korea would add another unfavorable coastline rather than a wholly new strategic condition. China also complicates any overland pressure, limiting the direct threat to the fleet base.