If your oil pressure light is intermittent, that is, some days it goes off normally and at other times it does not, then it is highly unlikely that the o-ring on the center bolt is the problem.
Everytime you run the engine, the check valve is pushed up. When you turn off the engine, the valve comes down on its seat. Everytime this happens, the valve can come down differently because it is free to rotate. Sometimes it may come down just right and when you start the car, the light is normal.
These were my symptoms with both canisters. I would say that 90% of the time the light took for ever but now and then, it would be fine.