You can buy the rubber seal at Home Depot. $2 for a pack of 10. There's a thread with details in the 6 series forum. They have the same issue with exact same part.

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2004 BMW 745Li e66
22" Beyern Mesh
Eibach Springs
Spacers 20mm Front 30mm Rear
Akebono Brake Pads
JL Audio 500/1 Amp
2 Type R 10" Subwoofers