Well, I've been down in gustav for over a week now. Solo'd this bastage several times and he still refuses to drop the bow.
What makes it worse is that at one point, I went afk to make a cup of tea and came back to see a couple guys duo'ing it. Low and behold, they got the drop, after only camping for a grand total of 2 minutes.
Once I get this bow, I'm not going back to Gustav for a loooooooong time.