WXLO evolved to a younger skewing Top 40 format and the "99X" moniker remained until late 1979, when it became "FM 99 WXLO." This iteration had decent ratings for a while, but by the spring of 1980, the ratings fell dramatically. RKO General phased out the Top 40 format, and brought in new Program Director Don Kelly from successful sister soft adult contemporary WFYR in Chicago in an attempt to duplicate that format's success on WXLO. The station at first attempted a call letter change back to WOR-FM, but an FCC challenge from competing crosstown WRFM (now WWPR-FM) prevented the call letter change from happening. Still, Kelly attempted to make the station the same adult contemporary format he had in Chicago. These changes did not gain any new listeners for WXLO, and ratings sank even lower. Later, Kelly adjusted the music and very slowly and gradually began mixing more disco and soul into the format. In the Fall of 1980, Kelly, in consultation with RKO General, decided to go after WBLS-FM's urban audience and WKTU's Rhythmic audience by bringing in new music director Barry Mayo. Mayo, shortly before his arrival, suggested a new format for the station to Kelly and then-general manager Lee S. Simonson after he received a surprising lambasting from his idol, WBLS Program Director Frankie Crocker (who would later become his rival). Mayo would later become WXLO's Program Director when Kelly left to start his own consultancy.