The correct answer is A) Reduce power to stay within limits. If the full power vibration limits are exceeded on a gas turbine engine, the appropriate action is to reduce power to bring the vibration levels back within the acceptable limits. This is necessary to prevent potential damage to the engine and maintain safe operation. Exceeding the vibration limits can lead to increased wear, component failures, and even catastrophic engine failure if not addressed promptly. The other options are not the correct actions in this scenario. Borescoping the engine (B) would not directly address the vibration issue, and water washing the engine (D) would not resolve the vibration problem. Doing nothing (C) is not an appropriate response, as it would allow the engine to continue operating outside of its safe vibration limits.