User blog comment:Omega natsu2/Chapter 372: Breach, Predictions./@comment-3424593-20140215230342/@comment-24066070-20140216000503

I doubt Lumen can just be "found", since Ivan searched every place located to the guild and never discovered it. Only the Master knows the spell to release the seal of Lumen's door.

About Makarov not appearing in the Cube yet, he is small so he may be behind the taller folks.