I too made heavy weather of this, but am pretty much there thanks in large part to the hints on here so thank you.
I have one remaining clue (and cell) to complete and that’s 13d. I’m guessing the first word has the letter change (I need the T). My best guess at the unchecked cell is M but I could be wrong. And I cannot parse it. I never quite parsed 16a either so maybe I’ve made an error there. Thanks