Any suggestions on what to do about a slow leak. I can fill it up and it'll last 2 weeks, come out in the morning and it's half flat. I can't find anything stuck in the tire. I wiggle and jerk the valve stem around expecting to hear air but nothing. Put spit on the valve core hoping to see bubles, nothing. It's starting to piss me off. I kinda hate to dump the fix-a-flat stuff in it but you think that's my best bet?