Yeah I used to work in a Firestone, and I have to agree with JK The green stuff really pisses you off when you go to pop the bead on the tire and there is just a slight bit of that crap in there thats still wet !!

Well anyway I was gonna say the same thing as him sometimes it's just easier to take it to your local tire store or garage have them check the stems and bead by dunking it that will usually tell ya where you got your leak.......... or you can do it the shade tree mechanic way I used to tell this to my friends when they had slow leakers.
Get you a spray bottle with about 3/4 full of water and then put you a couple of squirts of dishwashing soap in it, then mix it take it to your tires and you should find the leak pretty quick.... when you see your bubble show !!!
Well just my two pennies.
Later
Husker