I cannot for the life of me find out what o-ring this needs. I'm also unable to find any manufacturer or model number on it. The filter that I use is a unicel c8409. The pump I have is a Hayward super pump II. That filter says it fits a Hayward CX-900 but I've tried it and it's only 9" in diameter. It measures 11.5". It leaks around the rim of the cap when under pressure. Anyone know the fix?