A leak error always gives the name of the point entity nearest to it. This can often help in certain maps, in a recent NS one I managed to narrow down the leaks to my Ready Room, where the only info_player_start entities were in the map. If all your leaks are in the only point entity in the map, however, things get a bit more peachy. Use the pointfile to your advantage here, it can usually track down nasty (mostly) invisible leaks and if you have Hammer 3.5, it can show the pointfile in editor, which makes things easier too.