I have a Pentair FNS filter with a Hi-flow backwash valve. The valve top was cracked around the bolt holes and leaking so I replaced the valve top and the gasket. I adhesived the gasket in place and replaced the valve top. Now there is water leaking out of the backwash hose when the valve is set in filter mode. Everything seems to be installed correctly. The gasket matches the original one and the valve top is the correct one and the same as the one replaced. Any ideas on what is causing this and how to fix it? Thanks