I have seen many times that the belt tensioner fails right after being adjusted. This is especially true when the tensioner is old! The rubber will find a spot where it likes to travel and when a new alternator or belt is installed the tensioner fails. It is not the tech's fault when this happens, just an old part!! When I feel it is called for I write one on the estamate sheet to warn the customer in advance!!
ASE CERTIFIED MASTER AUTO TECHNICIAN
LEAD TECHNICIAN FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM