I can't answer Peter K's question (by the way, we met in person once, but I haven't seen him on Mudcat in years) but I think he would also be interested in this 44 min radio documentary I just listened to: https://www.bbc.co.uk/programmes/m00007jy The Bernstein Files

"For more than three decades the US government compiled covert reports on the political activities and associations of legendary conductor composer, Leonard Bernstein. ...
...
"Investigative reporter Jonathan Coffey travels to New York and Washington to open the secret FBI files on Leonard Bernstein and ask why the US Government spied him for more than three decades. ..."