Textron Aviation issued a service letter advising Cessna 172S owners to inspect the left and right rocker box washers at their next 100-hour or annual inspection. Certain models have been found to be missing these washers on the rocker covers, which could cause damage or cracking to the support bracket.
If the washers are missing the support bracket will also need to be inspected for cracks or other damage. Damaged brackets will need to be replaced and the washers correctly installed. If the washers are installed, the inspection should be noted in the logbook but no further action is needed.