What was found
WHILE PERFORMING 750-HOUR ANNUAL REQUIREMENTS INSPECTION, THE MAINTENANCE CREW FOUND THE AFT AND FORWARD MAIN ROTOR SERVO PISTONS ASSEMBLY (IN MID-STRIKE RANGE - ON GEARBOX SIDE) SURFACE PLATING STARTING TO DEGRADE. THERE WAS VISUAL SCORING THAT WAS COPPER COLOR, AND PITTING WHICH COULD BE FELT BY PASSING YOUR THUMB NAIL ACROSS THE PISTON SURFACE IN THE AFFECTIVE AREA. THIS AREA CAN ONLY BE VIEWED WITH EXTERNAL HYDRAULICS POWER APPLIED TO THE AIRCRAFT WITH COLLECTIVE CONTROL IN FULL UP POSITION, AND VIEWING THE SERVO PISTONS FROM THE GEARBOX SIDE.