You first need to know where its leaking.
Instead of dunking in water, I like windex. Sprat it around the bead. If in 5 minutes you have a bunch of foam, its the rib leaking.
Your options are pretty much as radioman said. Tube, Slime, or foam. But you MUST know where its leaking first. I have had good luck with slime sealing beads, but not so much for punctures. And if it is indeed punctured, once you slime it, a plug/patch dont hold well.
My front ags on my
L3400 leaked slowly around the bead. I slimmed them. And it worked for a few years before needing it again. And again, wit worked for a few years. This last time, I broke down and installed tubes:thumbsup: