I have never used them personally so I don't know if they leak. Mine is a disc so I am just rolling with that. 8.8 28 spline puts up with a fair amount a abuse so 31's in a light car should be fine but other will chime in I am sure
I would just use the stock axles maybe buy some c-clip eliminators, the car is so light I doubt it needs more than that. (Mine weighs more and has that setup )