Some important information, compliments of Bilstein Corporation of North America. Mr. Mark Anderson, the East Coast Regional Sales Manager, notes that, next to the Mercedes-Benz shock replacement market (Bilsteins are standard equipment on M-Bs), BMW replacement sales are one of the highest, and growing steadily. As their sales volume has grown, so has the return of front shocks for warranty replacement. According to Mark, most of the returned shocks are perfectly OK. The problem is the installation procedure. He emphasizes two points:

1. Don’t overtighten the retaining nut (the nut that locks the shock insert inside the McPherson strut). The recommended torque for the retaining nut is 87 ft-lbs. If more torque than this is used, you may jam the shock mechanism from the excessive pressure. My suggestion to him and you is to use some “Loctite” on the strut threads. This will help prevent loosening of the nut.
2. Do make sure the rubber boot and boot clamp (if provided) are installed. In winter, water can freeze on the piston, ultimately preventing the shock from compressing. If you hit a bump with a frozen (literally!) shock, you can do bad things not only to the shock, but also the suspension. Even thinking about this one hurts!