These holes varied between the different cases. There isn't any pressure on them, so if they drain, that's all it takes.
That said, sometimes I have found flash from a mold that some tech did not clean out: this often shows up in the "horror" pictures we occasionally see where someone cleaned their oil pan and found them, years later. It's usually some flash casting edge that escaped the initial sandblast treatment that was used to remove casting scale, etc., when the parts were once new. If it is flash, it will be thin enough that a good tap with a screwdriver tip will break through it: if so, then think about filing it away so it won't risk a trip through the gears someday?
