Most of the online MB parts stores have them (FastLane, buymbparts, etc), even the dealer might. I paid something like $13 for mine online. I just wish I was able to use it (apartment)

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Dan
2005 E320 CDI - 246k
1987 300SDL TD05-16g, Herlevi pump, Elbe manifold, 2.47 LSD - 213k
Past: 1987 300D - 264k