As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
EN ROUTE FROM BDL TO DTW, THE AIRCRAFT BEGAN AN UNCOMMANDED GRADUAL BANK. DISCONNECTED AUTOPILOT AND FOLLOWED COM PROCEDURES. REGAINED COMPLETE FREEDOM OF MOVEMENT OF CONTROLS PRIOR TO APPROACH AND LANDED WITHOUT INCIDENT. MAINTENANCE FOUND CHECK VALVE FOR LEFT SIDE SLANT PRESSURE PANEL DRAIN CLOGGED. CLEARED DRAINS AND REPLACED CHECK VALVE. AIRCRAFT RETURNED TO SERVICE.