Oil Leak at front case half bolts...

Looks like a crack.

Never seen a crack in that location before. Did someone over TQ the gearbox bolt or install a bolt that is too long?

Did you experience a propeller strike at some point?

When was the last time the gearbox was removed and serviced? 

Magnetic particle testing is used to detect cracks, 

Use this technique.if any crack, you may find it.

James N Parker wrote:

Jeffrey, looking closely at your picture...  It may be just a photographic illusion, but it looks like there a crack in the case next to that bolt hole, starting about the 9 o'clock position of the bolt, continuing around to the 6 o'clock position, and then straight down for a little ways...  

On the left from the red-line ?

Nope.  It's just to the right of the wide red line I added to the picture (updated by me, below).