I have just investigated a rattle underhood of my '93 300D and noticed that the tensioner roller is out of alignment with the serpentine belt. I suspect this the the source of the noise. Is it just the roller that would need to be replaced normally, or is it common to have to replace the entire tensioning assembly?

Thanks in advance.

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'01 CLK430 (hers)
'99 528iT (turd)
'87 Porsche 928 (just for fun)