Based on the picture they have, that part looks like the female piece that mounts to the windshield header, not the plastic clip that fits into that piece.

A cheap workaround is to buy the clip from a 126 Chassis. You would need to completely remove the broken clip and replace the female piece in the windshield header with the 126 clip. I've done this with my passenger visor. My driver's side visor recently broke (again) and I've temporarily removed it. I'm too tall to use it anyway.

I was given a lead about a guy who had designed a replacement clip, but he hasn't responded to my emails. How hard could it be to design a replacement piece?

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Mike Heath
1988 560SL Black/Palomino
1988 300SEL Black Pearl/Burgandy
1984 500SEC Anthracite Grey/Palomino