Does the car in question use a cartridge style filter like the 80s cars did, or does it use a spin-on filter? If it uses a spin-on filter, there are no O-rings to replace, you likely have a worn oil pump or something leaking down in the engine.

If you have a cartridge style filter, there are a couple of O-rings on the end of the central rod as mentioned above that will cause loss of oil pressure and leak-down of the oil filter housing.