AKA "door check". If it is like my '98 then it is made of metal. You can buy a new one but it will not be painted ,it will be goldish color. I tried rebuilding mine but it is very difficult. To remove it you have to remove the door panel and it is held with 3 bolts I think.

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1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra