oh boy
Based on my understanding of the issue as you described it the problem is not in the door check but the piece that the door check "pin" slides into on the jamb. Those pieces can break loose from their weld. The issue is fixing it. When you remove the pin it will fall down into the jamb area and you play heck fixing it. You have to remove the inner panel and then cut away metal to get in there behind it to replace the part that the pin goes into. Have to use a welder to put everything back together.

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Jim