I just went there today, went through the narrow hallway with the Iksar necros that automatically come out of their cells. Fought to the end...looked down the stairs; there was a "Lecherous Scarb" but no "Gangrenous Scarab". I stuck around and waited for to see if the respawn would give up the G. scarab . But that did not happen.
I am trying to get the "Staff of the Waterwalker".
Any suggestions?