That's the same as mine, my old ones anyway. The clip is missing, meaning there is nothing holding it in there except rust or it's just jammed. My van had two flanges in it, one with a clip, one missing when I got it. The clip is a pain anyway and that's why I suspect most are missing. As you can see the post stays in there just fine. I would soak it in WD-40 or the like and just wiggle it every day or so. If you take the whole flange out your problem will not be solved. It is sealed from the weather on the bottom, meaning you will have better leverage to get the post out while it's still mounted in the van as it is now. It's also cheap, light metal so it probably won't take much abuse before breaking.