As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CLIMBING OUT OF FL250, AIRCRAFT FISHTAILED LEFT AND RIGHT FOR 3 COMPLETE CYCLES. OSCILLATIONS CEASED WHEN YAW DAMPER TURNED OFF. NO FURTHER PROBLEMS. REMOVED AND REPLACED YAW DAMPER COUPLER AND RUDDER PCU PER BOEING MM. OPS AND LEAKS CK NORMAL.