Racewalker

Hi there. When recently having my 2006 TL serviced I was told that the half shaft bearing needs to be replaced. When inquiring I received minimal info as to 'why' this repair is necessary. My TL has ~78,000 miles which are mostly driven on the highway. There is no evidence of oil or any other fluid on the garage floor where the car is parked. Any thing I should know about the urgency for repair and/or things I should be looking for? Thanks for any info anyone can provide!