Just looking for some confirmation before I attempt this. I have the plastic pumps, and am wondering if I can pull out the old rubber OEM wear rings and replace them with the Derlin SBD rings by placing them in the freezer to shrink the rings. Or will the plastic pump just shrink with the rain? And do I have to pull the impeller prior to doing this way?. It appears that the YouTube videos they do not remove the impeller. Any help appreciated