Sorry, that was unclear of me, wasn't it?
What I meant was I did a G-search to find someone who had posted somewhere which category RM was under (Folk, which I suppose makes sense), rather than go through 500 radio stations (I have never found a search function in iTunes for Radio Stations). Then, I went to Radio->Folk and clicked on the 64 kbps link for RM, that worked. So, I dragged the 64 kbps link to a Playlist I made called "Radio Stations" and checked that clicking on that link still worked.
I have no idea why the RM item in the playlist that had been working for more than a year stopped working. None of the other radio stations in that playlist exhibited the same behavior.
By the way, it says 64 kbps, until I click on it - at which point it changes to 40 kbps.