Cessna parent company Textron Aviation issued service letter SEL-74-06 regarding reports of impulse coupling stop pins on Slick magnetos moving from their factory-installed locations. If the pins become liberated from their install positions, the part could enter the gear train of the engine leading to catastrophic engine failure.  

Affected magneto models must be inspected and/or replaced with approved replacement models at the next maintenance interval (not exceed the next 100 or 400 hours TIS) and every 500 hours thereafter.  

UPDATED: Download the service letter for a complete list of affected aircraft models and information about inspection procedures.