You can remove the internals and clean them, as you get corrosion on the tiny brass plate, spring and internal connection to the screwin part. The internal connecton part I clean with a sharpened long bladed screwdriver. I replace the Carbon resistor which can be prone to failure with the wire wound ones in the NGK caps. Unfortunately is usually means breaking open the NGK caps, but an NGK cap is a lot cheaper than OEM caps.