I was replacing the flapper portion of my Pentair check valve on my spa return line, but noticed it didn't quite seat flush all the way. There was maybe an 1/8"-1/16th" gap between the clear plastic face and the face of the flange on the black housing. When I screwed it in tighter to try and seat it flush, the gasket became mangled a bit from the pressure and squeezed/popped out a portion of the side between 2 of the screws. Is it normal for it to seat flat all the way? It's like the gasket is taking up too much space and won't allow it to seat flat all the way. The old one seated flat, but it was missing the rubber gasket (but it wasn't leaking from the face). Any help is appreciated. I attached a pic for reference.