Fine puzzle and the trickiest of the weekend for me. Huge thanks to Jaques.
I know that the final letter of the second word of advice has to come from 34 across, but I just don't see it. Despite having uncovered the device for the "disguise" I can't work it out from the message.
And finally, I almost disguised 21 down incorrectly since one of the unchecked letters gives two possibilities for a real word, but only one for the disguise to be complete.