What was found
AT FL390 WITH AUTO PILOT ON ACFT APPEARED TO BE DUTCH ROLLING. WITH AP OFF, ACFT AILERONS ARE VERY STIFF & DIFFICULT TO OPERATE. ROLLS STARTED AT 2 DEGREES & FINALLY WAS DOING 15 DEGREES. SAT WAS -60 AND DECENDED TO FL 270. PROBLEM GREATLY REDUCED WITH TEMP SAT - 30. APPROACH & LANDING, PROBLEM COMPLETLY RESOLVED. SERVICED AILERLON ARTIFICIAL FEEL SPRING UNIT. REMOVED OLD SILICONE GREASE & APPLIED NEW SILICONE GREASE. CYCLED AILERON SYSTEM SEVERAL TIMES & CHECKED SYSTEM FOR FULL & FREE MOVEMENT WITHOUT BINDING. ALL WORK IN REFERENCE TO MM 27-10-35