After many occurances of having to drive miles across town to help my daughter with a flat tire, I stocked her car with these cans. They work fine in most cases.
I would agree that the thread here would support a rim leak. Sometimes a bad valve stem will do the same, because they seal in the same way as the sidewall does. Occasionally you will find one with a crack or bad stem core.
Being careful to dress the rim contact area for both sidewalls and valve stems, and replace the stems, the problem should be fixed.