https://www.youtube.com/watch?v=VxU9TuPQSUE
Nice little interview with Dave Walker. He talks about FM for about a minute from the 4:00.
His recollection of the reason for him joining is interesting- he says that in addition to Danny Kirwan having left, Bob Welch was supposedly going to leave as well, which of course didn't happen for another couple of years or so.