Rearend trouble! HELP!!!

So i get underneath my truck to check and make sure everything is okay and i look at one of my two link bars and its wet with oil out of my rear axl. it looks like its coming out underneath or between where the u-bolts meet the two link bar. its not a lot yet, but i need to get it fixed right away. do i just take it apart and weld it back up if its cracked? What causes this? Any info is greatly appreciated. Thanks.