A brief update for what it's worth.

The replacement 24mm TS-E arrived a few days ago. I shot a series of comparison test shots with my 17-40 as before and the new TS-E is pretty much the same as the first one. I was half expecting this as I suspected there was nothing wrong with the first one.

I guess my interpretation of the reviews of the Mk II TS-E on this forum and others led me to expect too much. Have no doubt the TS-E at 24 is always better than the 17-40 at 24mm but not as much as I expected/wanted.

So, nothing left to do now but to get out there and shoot.