Extraction problems on old winchester defender

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I have a really old and well used Winchester Defender (Department of Corrections retiree) and it has developed an extraction problem. I looked over the extractor and it doesn't look broken or anything. If I cycle the bolt slowly, I can watch the shell actually move out from under the extrator when it is about half way out of the chamber. Is there something missing on the other side of the shell that is supposed to hold it in place? I am not too familiar with this shotgun, mostly shoot 870's. Thanks for the halp.