Finally, after researching all the available products, put the recommended amount of this goo into my rear tyre and went for a brief ride to circulate it.
After a week, while I’ve been on a business trip, 38 degrees in Normandy yuk!, no tyre pressure loss. Before it was about 2 psi per day. Apparently the stuff does not go off so I may treat the front tyre. Yeeha!