*rolleyes*

If it isn't lugged take it to a specialty welder and get it TIGed back together. MIG, even if done very carefully, doesn't have the heat control to melt the old weld while maintaining an adequately "cool" temperature on the original base metal without making the weld brittle.

If it has sentimental value, expect to pay 75-100 bucks for a decent job by a pro-welder that knows the ins and outs of welding dissimilar metals. Pay 10-15 bucks for a hack job the will probably end up cracking again in a few months