Metering rod piston can be replaced with a new one. The throttle shaft can be re-bushed. And "top distortion" you mean where the top of the carb mates to the fuel bowl, the surface can be sanded down on a belt sander. I have not done this on my BBD yet (resurface)...but I may need to. As long as you have all the tools, all of these should be able to be done for around $10 in parts.