As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AT FL390 WITH AUTOPILOT ON THE ACFT APPEARED TO BE DUTCH ROLLING. WITH AP OFF, ACFT AILERONS ARE VERY STIFF AND DIFFICULT TO OPERATE. ROLLS STARTED AT 2 DEGREES AND FINALLY WAS DOING 15 DEGREES. SAT WAS -60 AND WHEN WE DESCENDED TO FL 270 THE PROBLEM WAS GREATLY REDUCED WITH TEMP SAT - 30. APPROACH AND LANDING THE PROBLEM COMPLETELY RESOLVED.