Aye, the 3 percent spawn rate seems right to me.
I killed him 3 times before he dropped the augment. He dropped the earring every time.
Twice he popped in the front cave with the dual mobs in it.
The last time it was one of the single mobs on the beach. Kind of surprised me.

Goblin Skull
Pearl
Shard of Dark Earth
Sharp Fang Earring
Water Totem Piece
