I've been working in the marine industry for more than 25 years as an engineer, and I have used permatex on many occasions with good results. I haven't tried the ultra black, but as long as the surfaces are clean, and you don't applt too heavy of a bead along the sealing edges, I thing it will be OK. However, NEVER use the permatex hardening type gasket maker, as it is a real B%$ch to remove from the joint faces.