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I'm the proud, new owner of 1963 M20C, N6578U since yesterday. The prop is of the older Hartzell "non-suffix" hub with the 100 hr recurring AD for an eddy current inspection. During the pre-purchase survey earlier this week at Advanced Aircraft Services, I had expressed interest in having the prop overhauled if I bought the airplane. AAS' neighbors at Western Aircraft Propeller alerted me to a recent Aug 27, 2012 update to Hartzell service bulletin HC-SB-61-269 "Propeller - Hub Inspection." The update is significant in that it adds an FAA-approved alternate means of compliance that effectively eliminates the eddy current inspection requirement WITHOUT a costly upgrade to the B-hub. The service bulletin is updated to include an Optional Terminating Action for the hub inspection by "modification of the propeller hub to the oil-filled configuration in accordance with Hartzell Service Letter HC-SL-61-273." According to SL 273, "Converting the propeller to an oil-filled configuration will provide a method for early detection of a possible crack in the hub. The hub cavity will be filled with oil that contains a red dye. If a crack in the hub occurs, the red dyed oil will provide a visual indication" At ~$3300, the cost of an overhaul and incorporation of SL 273 kit falls about halfway between that of a prop over haul and that of a normal prop overhaul with upgrade to the B-hub. Work on my airplane's prop overhaul and SL 273 incorporation commences next week. Page from HC-SL-61-273.pdf HC-SB-61-269.pdf