Late to the party as ever, but finished it with help from several gentle nudges ... including the very first post where "I'm a fan" made a connection!
But, if anyone still around, where do the last 2 letters of 23a come from? From a late forum post I now understand the first 3, and it showed which of two possible "college" answers was the right one, but ... ?
FOI: 18a
COD: the very clever 23d
LOI: 23a
A tricky one, but when I picked it up again today I suddenly saw 5d and went on to crack the other remaining mysteries with help from here. Thanks!