A vented cap for a main spring housing of a slack adjuster including an inner portion having an inner seal surface configured for cooperating with an elongated rod member and an outer seal surface configured for cooperating with a sidewall located at an end portion of the main spring housing. The vented end cap includes at least one opening configured to allow fluid and/or contaminants trapped within the slack adjuster and/or the end cap to drain therethrough. Various seals and/or drainage openings can also be provided along the slack adjuster to prevent the entrance of and/or allow for drainage of fluid/contaminants from the slack adjuster. A method for preventing the accumulation of fluid and/or contaminants within a slack adjuster and for protecting a critical operating area of the slack adjuster is also provided.