A distributor cap doesn't have to be replaced just because it has some miles. If the wear is minor, it can be cleaned & used again. The corrosion is brittle, and can be chipped off as a flake using a pocket screwdriver or pick. Then the terminal can be shined using sandpaper, steel wool, or a Dremel-type wirewheel.
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Applying silicone grease inside the cap (as Ford recommends here) will repel water, allowing the engine to run even if the distributor is splashed. Applying dielectric grease to the tip of the rotor will reduce the ozone corrosion on it & the cap's terminals. Never apply dielectric grease to the graphite contact, its mating contact on the rotor, or to any electrical connection. A Rubber Distributor Cover E6TZ-12252-A will also help repel splashed or sprayed water.

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Owner caption March 2019 · Photo 0 of 5000