I had a leak at the point where the manifold valley and head meet. I tried different sealants (ultra black rtv, etc) and gasket combinations, to no avail. My nephew is a service manager for Toyota, he suggested a sealant they use for
oil pans, camshaft housings, etc, without gaskets. I used Hitac on both sides of the head/manifold gasket ( as I had problems with that gasket being sucked into the intake port between the intake and water jacket port because of the narrow space with the stageIII head port job). I used the Toyota sealant in place of the valley gasket and up onto the lower edge of the head/manifold gasket. No more leaks. The Toyota part #00295-00103. Try it, the stuff is awsome. Make sure you let it cure for 24 hours before firing up and apply a thick layer (1/4"), you can trim off the excess after a couple of days.