I have an older in-ground Blue Haven pool. The pool was built in about 1992 and is in very good condition. The filter is a Hayward Starclear II C1100 single cartridge filter which I believe to be as old as the pool. I replaced the pump last year and keep the cartridge clean and it all seems to work very well. Recently it began to leak from the o-ring between the filter body and the filter head. The o-ring was replaced but the leak continued. At that point I began to check everything closer and discovered some hairline cracks in the filter head. I had read they could be fixed with epoxy or JB weld but decided to purchase a new filter head. I checked the filter body and found no defects and another new o-ring was used with the new filter head. When started with the new parts it still leaks from the joint. The filter body seems level and there are no visible defects. The water seems to be pushing out from around the o-ring. The gauge in the new filter head indicates the pressure in the system is where it has always been and there is nothing else that has been changed. I have tried it with o-ring lube, different tension on the locking nut and anything else I can think of but this leak wont stop. When I close the system it does not leak initially but as soon as the air purges from the system through the returns the leak comes back. Has anybody experienced this before and if so, what fixed it. I would hate to have to purchase the entire filter system because I cant get the o-ring to seal.