I have removed ball valves after years of use and not had that much build up. I always clean my kettle and ball valve assembly thoroughly after brewing with a hot (160F) powdered dishwasher detergent-based solution. I never disassemble my ball valve. I just allow the solution to work for 20 minutes with valve closed and 15 minutes with the valve open and a clamped section of tubing attached to the outlet. I then rinse the kettle, fill it with a couple of gallons of hot water, and allow the water to drain through the ball valve. I leave my ball valves in the open position, so that air will flow through the valve while drying. An ounce of prevention is worth a pound of cure.