If you are removing the Tensioner Assembly be sure to clean all the threads of the locating bolt and those in the block for the main bolt. Use Loctite on these threads when you reassemble and torque to factory specs. Like Brian, don't ask why I know this

Check the tensioner Shock-absorber as chances are it will need replacement as they don't seem to have a long service life.

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1991 M-B 560SEL Arctic White/Grey 99,000 Miles
1987 M-B 300SDL Ivory/Palomino 229,000 Miles (sold but never forgotten)
2006 Volvo XC70 Blue/Beige
1999 Porsche Boxster Arena Red/Savanna Beige
1986 Porsche 928S Goldweiss/Brown