Hi Widget,
I have only ever swapped out one "O" ring on the inlet manifold and that was because it had a chunk out of it. The washer under the cam is to help shut the poppet to bring the idle down, another mod because the so called design engineers put lumps on top of the cam. I sometimes change the "0" ring on the starter depending on how I feel, sometimes I just put a smear of silicone on it, works fine
