I checked with the S-76 Chief Pilot, and he told me this:
Recently, one aircraft had difficulty with the stabilizer attachment bolts loostening up (not holding torque). They tightened them up several times before replacing them. In the interim, the lose stab caused high loads in the local area, which caused the cracks. A service bulletin will be out shortly on this.
This is the first such incident in the several million hours for the S-76 fleet.