you could have it welded. Not sure if that is the best fix if you have something serious going on there, but its good for stiffining up the assembly also.
Mine was seeping a bit, so I cleaned it up really good and put black RTV around it and its been good to go, but my leak was really very minor, just a small wet spot nothing dripping.
They are a very tight press fit. Something pro racers do before jumping to the ford 9" is indeed weld the axle tubes to the housing as this is not done in factory form. A major thing one must do is make sure there are no hairline cracks of any type in the axle tubes or the housing - if this is the case then whatever you do to try and fix it is time wasted from then on.