Checking the sealing ring
WARNING: This page does not describe the selected car, but rather 8 other vehicles, including the 2006 Volvo S80, 2005 Volvo S80, 2004 Volvo S80, 2003 Volvo S80, and 2002 Volvo S80. However, it is still accessible from the selected car via links, so may be relevant.
Check that the sealing ring in the gearbox end is undamaged.
Replace the sealing ring with a new sealing ring if damaged, see Remove the drive shaft seal and /or Install the drive shaft seal .