M112 belt tensioner pulley vibration

The belt tensioner pulley on my S350 2004 is vibrating more than expected: What do you think? Should I replace just the pulley or the entire tensioner? Is the tensioner at fault or perhaps some other pulley is introducing resistance that makes the belt tensioner to vibrate?

The belt tensioner pulley on my S350 2004 is vibrating more than expected:

What do you think? Should I replace just the pulley or the entire tensioner? Is the tensioner at fault or perhaps some other pulley is introducing resistance that makes the belt tensioner to vibrate?

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