On my SDL the main tensioner assembly locating bolt had unscrewed itself from the block causing the tensioner to tilt. Be sure to use some 'Loctite' on the threads of both the main bolt and the pulley bolt when reassembling.

By the way, you can undo the Allen Bolt holding the Fan without removing the Radiator if you have patience and don't mind a few scraped knuckles

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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