I've swapped rear ends before but never really taken one apart. I broke a tooth on my ring gear, its a stock 9 bolt with 4.11 gear set. Any advice on if I should try to fix it or just buy an aftermarket rear? I'm probably pushing 400HP to the wheels with 315 drag radials so there is a fair bit of stress on the rear.

 

A 12 bolt would hold up much better. I'd say that you are at or just above the limit for what that rear end can handle. A 12 bolt isn't cheap, but neither is replacing gears all the time.