What was found
(CAN) FROZEN AILERONS AT FL280 CLIMBING TO FL300. A/C WAS STILL CONTROLLABLE BUT ONLY WITH A BANK ANGLE OF 5 DEG. DECIDED TO START A STRAIT DESCENT DOWN TO FL70 TO GET OUT OF FREEZING LEVEL. AT FL70 AILERON OPERATION WAS REGAINED. LANDING IN DUS WAS NORMAL. BEFORE FLIGHT, HAD HEAVY RAIN SHOWERS. FDR REPLACED. FOUND 'GEL' ON AILERON FLT CONTROL CABLE PULLEYS. CLEANED PULLEYS AND APPLIED LPS 3 TO CABLES IAW MM 20-23-00.