Small crack in block

I noticed some oil on the (top)passenger side of the engine on my son's 2006 Subaru Outback (about one tablespoon). It is not from the oil sending unit. He brought the car in to a Subaru dealer in MA, to check it out and they told him it has a small crack in the top of the block. They estimate approximately $5000 for a short block (inc. Labor) or $2500 for a used engine.

I believe he needs to get a second opinion. Does a crack in the block seem a possibility? (In the last 1600 miles traveled, the oil still measures full.) If not, what do you think may be the problem?