I don't know if all pistol magazines are made the same but 2 out of the 3 'leak free' mags I got with my P226 leaked. I stripped them as far as I could, didn't have a valve key, and soaked the base O ring in silicone oil for a couple of hours and added a few drops of the same to the valves. All three are now leak free.
Interestingly, I used the bottle of silicone oil that came with my beard trimmer, so nothing special or expensive.