Leaking Hayward S 240 filter

Hi...a few months back I noticed a drip from the bulkhead fittings on the filter..it was coming from between the filter and the fitting..mostly the top supply fitting. I have since replaced 4 O rings and two new bulkhead fittings and still it drips.. While I had the filter open I replaced 300 pounds of sand and the main large O ring that seals the top... it appears that the side o rings are not completely sealing..I hesitate to use any gasket compound or other sealant, It appears that the O rings on the valve assembly hold tight but the ones between the fitting and side wall of the filter are not sealing.. I have tried different degrees of torquing the fittings...I thought I had it solved , i ran the pumps for 12 hours and not a drip. i turned it on the next morning and the drip returned and everything was still tight..Can the openings have worn enough to make the O-rings ineffective?? will fatter o rings help?, I tried rubber flat washers instead and that was a complete disaster.. Do i really need a new filter?..This one is circa 1985..It is indoors and does not ever freeze . Thank You.. it's great having discovered this forum