Ok, I had my second flat tire in less than 6 months and on inspection there was no nail or obvious damage to the tire. The first time I just filled the flat tire up with air and it didn't leak. This time it was a different tire and when I put air in I could tell that air was leaking out of the valve stem. Looking into the stem to see if something was lodged inside I noticed that besides the pin there was a thin flat metal piece that was fitted in the hole around the pin and went from one side to the other. I took a paper clip and fashioned a tool from the two ends so i could insert it in the stem and use it to turn the flat metal piece. I noticed it was very loose and would spin around quite easily, so on a hunch I tried tightening it in a clockwise direction and after doing so the air stopped leaking out from the stem. I don't know anything about the design of the valve stem but Im guessing that if these things become loose the seal might not be air tight and this could be the cause of loosing air in a tire that has no punctures. If anyone knows if this is normal or if this is a defect chime in. I'm thinking that I have to keep and eye on this and check it every now and then to make sure it hasn't gotten loose.