That happened to one of my trunk stops years ago, but I've still been able to remove them by slightly squeezing with channel lock pliers. The worse case is that the plastic piece separates from the brass threaded sleeve that's inside it. But then you can easily remove the brass piece with pliers and epoxy them together. That's what I did with both of mine when the second trunk stop gave out as well. I washed and dried the brass and plastic pieces really well, then trimmed some of the plastic that goes around the brass sleeve for better adhesion. Used 2-part epoxy that mixes itself through the tube as you squeeze the plunger. After letting them dry overnight they were better than new. I should have taken some pics, but I didn't.