From the research I did
for the KWKW Wikipedia page (which I only mention because it now has an ungodly number of citations) Santana started working part-time at KFAC c. 1976, then got upped to fulltime in 1987 when the Heifetz-Argow-Goldfarb team bought KFAC and fired all the tenured staff.
I remember seeing Santana as part of the online-only iteration of K-Mozart as late as last year?
As for voice-tracking, KFAC and KFAC-FM had to do it at both stations when the programming was split in 1970; IIRC, Fred Crane hosted mornings on KFAC and voice-tracked KFAC-FM overnights. Cassidy simply preceded everyone else in the trend.