I think the OP is talking about an aftermarket clip that replaces the moving part on the regulator. I've seen them but did the whole regulator when needed. Perhaps the OP can put up a link? What problem are you trying to fix?

There is another smaller plastic clip that holds the glass to the moving piece on the regulator. Those do break but are available from the dealer, along with the a funny shaped nut that fits it.

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David.X5
2001 X5 4.4i Sport
SOLD! at 160k miles