A B737-200 CAPT INITIALLY EXPERIENCED A FLAP PROB WHICH CONTRIBUTED TO A WRONG RWY APCH.

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WHILE ON FINAL APCH INTO SJC; FLAPS 30 DEGS WAS SELECTED. I NOTICED WHILE GOING PAST FLAPS 10 DEGS THE ACFT EQUIPPED MORE AND MORE R AILERON TO KEEP WINGS LEVEL (UP TO 20 DEGS). PWR SETTING WAS NOTED EQUAL; WIND WAS NO FACTOR; FLAP INDICATOR SHOWED NO SPLIT FLAP AND OVERHEAD FLAP INDICATOR SHOWED NORMAL INDICATION. WHILE CHKING PROB; ACFT DRIFTED TO RWY 30R CTRLINE. FO NOTED LINE UP PROB AND THEN TWR; SO I CORRECTED BACK TO RWY 30L CTRLINE AND LANDED WITHOUT INCIDENT. THE ACFT WAS FLOWN 1 LEG EARLIER (SAT TO PHX) BY THE FO. WHEN LNDG IN PHX; THE WIND WAS HIGHLY VARIABLE WITH DUST STORMS IN THE OUTLYING AREA; SO IT WAS HARD TO DETERMINE IF THE PROB EXISTED ON THE PREVIOUS FLT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THAT THERE WERE NO INDICATIONS ON THE FLT DECK OF A SPLIT FLAP CONDITION. HE FOLLOWED THE STATUS OF THE ACFT AND FOUND OUT THAT THE NEXT DAY; DURING A FERRY FLT; 2 MAINT TECHNICIANS WERE ON BOARD. AS THE FLAPS WERE EXTENDED; EACH TECHNICIAN MONITORED THE FLAPS FROM INSIDE THE ACFT. THOUGH NO SPLIT FLAP INDICATIONS WERE NOTED ON THE FLT DECK; ONE OF THE FLAPS KEPT COMING UP. THE RPTR STATED THAT THE ACFT WAS DOWN FOR MAINT FOR 2 OR MORE DAYS. THIS WAS HIS FIRST EXPERIENCE WITH A SPLIT FLAP PROB ON A B737.