When I bought my 1950 8N, the shutoff knob was missing. I replaced the valve stem and the new knob. After an hour running, the knob and screw has fallen off. Any clue as to where to buy a new knob and screw? I really appreciate this Club, as the articles have been very helpful. I also own a 1951 Huber Maintainer, which has a 6 cylinder Hercules QXB-5 engine.