Had the same problem after I had the tires balanced. One was stripped and damaging the bolt, making it unusable. Tapped it and all is fine now, it took me literally five minutes. Those alllu wheels are really soft.

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1979 Black on Black, 300CD (sold), 1990 Black 300SE, Silver 1989 Volvo 780, 1988 300CE (vanished by the hands of a girlfriend), 1992 300CE (Rescue).