I will need to have another look, but I think 19d is a homophone of faulty. Basil Fawlty was played by John Cleese, hence the “I say, I say”.
As I recall “mead” and “code” were both sorted by “drink” and “end of “desipere” in loco”, and “on the highway” and “hundred lines” respectively. That left “thus” and “lear”. The definitions appeared to be “as demonstrated” and “king”. So that left wordplay for the pair as “sage gave (a)” and “25 for”, somehow.
That was my recollection, anyway. It’s a while since I thought about it.
Thales was one of the Seven Sages, but I couldn’t quite make that work.
Maybe you can fill in some of my gaps