Very sad, one of my heroes bites the dust. As a retired electrician I adapted Wichita Lineman as my theme song. Used to sing it at work all the time. And we called my boss the Rhinestone Cowboy because he was rich and bought himself a 711 acre ranch near Paso Robles. Glen was an outrageously great guitar player, one of the Wrecking Crew and he played on a lot of Beach Boys stuff too. Just last year I watched the excellent documentary on Netflix called 'It'll Be Me' from 2014 and it tells all about his career and his Alzheimer's problems. If you like Glen you will not want to miss it. Or you can watch it on YouTube for $3.99.
https://youtu.be/x-6Vjzq8dAk