What was found
UPON LEAVING 10,000 FT ASKING FOR CLIMB CK, AIRCRAFT EXPERIENCED A UNCONTROLLED RIGHT TURN, AS IF FLYING IN ANOTHER A/C WAKE. CK WITH ATC TO VERIFY POSSIBLE TRAFFIC. SHORTLY AFTER INITIAL TURN UNCONTROLLED AND UNCOMMANDED FLIGHT CONDITIONS (YAW AND ROLL) INCREASED IN FREQUENCY, UNABLE TO CONTROL A/C HDG/ALT. DECLARED EMERGENCY AND RETURN TO BSM WITH PROBLEM PERSISTING ALL WAY TO GROUND. DEFERRED AUTO FLIGHT/YAW DAMPER SYSTEM IAW MEL 22-2 CAT C CONTROL NR 805312. REMOVED AND REPLACED RUDDER TRANSFER VALVE, OPS CHECKS LEAK CHECKS GOOD CLEARS DMI 805312 PLACARD REMOVED.