As I see it, ya got two options.
Pull the rear and replace it.
Arc weld the cracks with the vent open. If they are along the center part of the bango.
If you can not weld, take it to a rear end shop and let them weld it.
cracks are generally a sign of excessive stress. I have heard of guys welding donuts around the tubes and across the bango to prevent this. I personally have not seen this myself.
Hope you get this fixed without more fun and excitement.
Trularin
