The rudder trim wheel on one of our G1000 aircraft was found frozen in the neutral position. Cause was determined to be lack of lubrication of the idler sprocket shaft located behind the trim wheel. The service manual is not specific on the lubrication of this item but calls for lubrication "as required" during the 100 hour/annual. NHQ/LGM will notify all our contract maintenance shops concerning this issue. However, Wings not yet under contract should insure their local shops are notified.