What was found
WHILE REMOVING BOTH WINGS FROM ACFT, FOUND FORWARD WING ATTACH BOLT EXTREMELY DIFFICULT TO TURN. AFTER LUBRICATION, BOLT STILL HARD TO TURN. AFTER BOLT WAS REMOVED, PLATING WAS OBSERVED TO BE GONE, THE BOLT WAS BENT, AND IT HAD SEVERE PITTING FROM RUST, WITH A POSSIBLE CRACK. AT LEAST ONE OTHER WING ATTACH BOLT FROM THE SAME ACFT HAS THIS SITUATION. SUBMITTER RECOMMENDS WING ATTACHMENT BOLT INSPECTION AT PERIODIC INTERVALS. LUBRICATING BOLTS UPON INSTALLATION SHOULD BE ACCOMPLISHED. NOTE: THIS CONDITION COULD ONLY BE OBSERVED BY REMOVAL OF THE BOLT. THIS PARTICULAR AIRCRAFT SHOWED NO EXTERNAL SIGNS OF THIS DETERIORATION.