Speedy the small "O" ring I have come across some missing (been removed by somebody) and sometimes I have needed the manifold for another motor, or if I have honed the bore, apart from that I usually just check that the screws are tight. As for the friction spring? do you mean the return spring in the pull starter. Never bothered with them, I have so many motors sitting here if I have a pull start problem I just put another one on. They are probably the easiest pull start to replace a cord on.
