WAKE TURB ENCOUNTER.

Narrative

COMING DOWN ILS ON RWY 25L AND CLRED FOR THE APCH AT ABOUT 25 DME THE ACFT STARTED TO ROLL TO THE R. THE AUTOPLT RECOVERED INITIALLY BUT AN INSTANT LATER; IT STARTED TO ROLL TO THE R AGAIN. THIS TIME THE ROLL CONTINUED PAST 15 DEG BANK AND THE AUTOPLT SEEMED TO BE STRUGGLING; SO I DISCONNECTED THE AUTOPLT; INCREASED THRUST; AND RECOVERED WITH AILERONS. AT NO TIME DID BANK ANGLE EXCEED 20 DEGS. ALTHOUGH WE WERE AWARE OF TFC AHEAD; WE WERE NOT ADVISED THAT IT WAS A B-757 UNTIL AFTER THE EVENT. SHORTLY AFTERWARD WE WERE ADVISED OF B757 8 MI AHEAD. HOWEVER; HE MUST HAVE BEEN VERY SLOW; BECAUSE WE CLOSED THE GAP RAPIDLY AT ONLY 210 KIAS. REMAINDER OF FLT WAS UNEVENTFUL AS WE STAYED 1 DOT ABOVE GS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR PARTICIPATED IN WAKE TURB CALLBACK AND WAS QUITE KNOWLEDGEABLE IN WAKE TURB RECOGNITION; AVOIDANCE AND RECOVERY TECHNIQUES. THE RPTR STATED THAT BECAUSE OF THE HIGH VOLUME OF TFC; THEY WERE IN A HIGH STATE OF AWARENESS; BUT DID NOT REALIZE THAT THE B-757 WAS ABOVE GLIDE PATH AND DSNDING THROUGH THEIR FLT PATH.