I have a Westinghouse stove from the 1970's that works just fine EXCEPT the knob for the oven. When it's "off" it's not going to the actual off position on the knob and it doesn't start turning on until it the knob is at the 350° mark. So unless I have an oven thermometer I never know what the oven temp is. I don't know how to take the knob off to see if I can fix it. Any ideas?