This is a very well made replacement for the traditional corroded plastic stock. Don't worry about installing with the included o-ring. This is an oversized and cheap rubber that doesn't fit properly. After lubricating and installing I took a mirror and looked at the underside where there is no screw and indeed there is a gap where the o-ring refuses to compress enough to fit properly. I took it off and found the o-ring was pinched, cut and torn. Do yourself a favor and buy BMW's standard for $6 or you'll end up there again. Too bad because it's a decent product even if it's from China, but that's how they understand you!