I think I figured this out...It was to some degree the 'white clip' from eBay that squeasel refers. The usually black clip that fits in the hole in the glass has a lip that must fit over top of the tab on the big white eBay clip. I got it to seat above with diligence, but probably would trim it a bit if it were not already installed.

By not having the black clip lip seated above, there is a gap between the glass and the white clip, that caused the attachment to lose grip and fail.

Assume this is resolved unless I report back.

BTW, I did have some challenge getting the cable 'bud' to seat into the white eBay clips. By rotating the clip or cable so that its metal 'buds' somewhat four sides slid into the somewhat square receptor on the clip solved the difficultly - once so aligned, I pressed it in fully with a small flat blade screw driver.

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2003 X5 Sport w/Premium Package M54 3.0L 6cyl