Ahoy I fought invisible leaks for several months (used all the cheap stuff) and nothing worked until I used the Inflatable Sealant from West Marine...It stopped the leaks right away. Here's a link to the product; http://www.westmarine.com/webapp/wcs/stores/servlet/SiteSearchView?catalogId=10001&Ntx=mode+matchallpartial&keyword=inflatable+sealant&Ntt=inflatable+sealant&N=377+710&storeId=10001&Ntk=Primary+Search&ddkey=SiteSearch

BobL