Thrust Block Is Broken
WARNING: This page does not describe the selected car, but rather 58 other vehicles, including the 2003 Saturn Vue, 2003 Saturn L300, 2003 Saturn Ion 3, 2003 Saturn Ion 2, and 2003 Saturn Ion 1. However, it is still accessible from the selected car via links, so may be relevant.
Replace the thrust block with a block of identical thickness. Check closely for other damage. See LOCKING DIFFERENTIAL DISASSEMBLE and LOCKING DIFFERENTIAL ASSEMBLE in appropriate OVERHAUL article.