Solved Tim
I was under the impression that Moodle needed all wildcards to be available in the question text, and maybe that was the case in version 1.
But, I've erased the comment hiding the right answer in the xml file, and Moodle presents the question in a correct way without any trace of 'the right anwswer'.
The trick the use {= } is relative new to me, but as you write would be a top alternative to obfuscate variables.
So the answer to "... to ensure that all the variables are mentioned in the question text, so that Moodle knows they are there. I am not sure that is really necessary" = It is not necessary!
I will adjust the googlesite.
Thanks Tim and Pierre for being critical. I should have shared this a few years ago...
Cheers
Hiram