I'm not sure how to contact Thierry directly. I did some searches and I can see the first part of his email address, but not the second.
I didn't test the individual outputs. I should have before removing all the pots.
I decided to go with the ones from Digikey I listed.
I already replaced one of them some time ago and it works perfectly.
Basically solder it, then bend it over. It's nice because I can control exactly where the shaft will end up to match the cover.
Thanks for the link to Small Bear. I may buy knobs from them or make my own. I have a small hobby lathe for metal work.
2 pots were definitely flaky. I will feel better knowing they are all new.
Rich