I'm very sad to hear this - I don't think John could have been older than his late 60s or early 70s. As a person who reveres a few dozen DJs from the "Top 40," CHR, and "free-form" FM eras in Los Angeles and San Francisco, I consider JMF one of the best. The photo of him on the All Access article says "KFRC 1992," but I think it had to have been more like '82., or earlier. My memory is less than perfect...certainly not Hagertyish, but IIRC, John was at KFRC during its greatest years of success in the early and mid 70s, then worked (K)CBS-FM playing Oldies, KSFO/KYA-FM, playing Oldies, KWSS - a South Bay CHR FM station in the 80s, K-101 for awhile, K-Big 98.1 in the early 90s, and I believe his last gig may have been country music at "Young Country," (formerly KYA-FM) when CBS briefly tried a country format. It always bugged me that CBS didn't move John over to 99.7 KFRC during their successful run as an Oldies station from about 95-04. It would have been a perfect fit.
After radio, JMF did work in corporate security, and returned briefly to the ill-fated 106.9 KFRC (now a repeater for KCBS-AM) to do the Sunday morning Beatles show - about 2005, or so. I never met John, but from stories I have heard, he was a very good man.