Can you take your hand and move the wiper manually? The bolt you talk about moving, is that the nut that holds the wiper on. If so maybe it just needs tightning up or it might be stripped.

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1995 S-350
370K + SOLD
1952 220B Cabriolet
39K kilometers + SOLD
1998 E300D
310K +
2012 E350 BlueTec
120K