I really like the kit from regulatorfix.com . He sends you the clips for all 4 windows, which is nice since you'll need them eventually. They're inexpensive, and I think his are a little stronger than the OE clips, too.

Edit: it looks like he no longer sells them all together as before. Still would recommend. BTW, his website is wonky.... just search for BMW, not for E53.

AM.

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E70 2010 3.0 M57 AT Titanium Silver with Black Leather
E53 2004 3.0 M54 AT Toledo Blue with Gray Leather
E83 2008 3.0 N52 AT Silver Gray Metallic with Black Vinyl
E46 1999 2.8 M52TU 5MT Black with Tan Leather 250K+ miles (Sold, but not forgotten)