Sounds like lower control arm bracket, indeed the factory ones are prone to bending/cracking. Personally I have seen it happen a few times.
Yes it can be safely re-welded (You're best bet is to replace with better brackets though).
No need to replace the axle tube.
On my XJ's Dana30, I went with a new pair of brackets from Iron Rock Off Road, but can't for the life of me find a link to them. They're made of much thicker metal than the stock brackets are.
A quick google search and I found these, which look even better, as they also have a built-in skid plate on the bottom for extra protection:
http://www.artecindustries.com/TJ-3044-HD-Lower-Control-Arm-Brackets-pair_p_372.htmlAnd yes they ship to Canada!