Make sure the ends of the Allen Wrench or the 12 point are flat. See post #20 for pics in the below thread.
They often have too much of a tapered beveled area that reduces the area that they can make contact with.
http://www.peachparts.com/shopforum/showthread.php?t=260567&page=2

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84 300D, 82 Volvo 244Gl Diesel